Elon Musk has clinched a deal to buy Twitter for $US44 billion ($A61 billion) cash in a transaction that will shift control of the social media platform populated by millions of users and global leaders to the world's richest person.

It is a seminal moment for the 16-year-old company, which emerged as one of the world's most influential public squares and now faces a string of challenges.

Musk has criticised Twitter's moderation, calling himself a free-speech absolutist, said that Twitter's algorithm for prioritising tweets should be public, and has criticised giving too much power on the service to corporations that advertise.

Political activists expect that a Musk regime will mean less moderation and reinstatement of banned individuals including former president Donald Trump.

Conservatives cheered the prospect of fewer controls while some human rights activists voiced fears of a rise in hate speech.

Musk himself has described user-friendly tweaks to the service, such as an edit button and defeating "spam bots".

Discussions over the deal accelerated at the weekend after Musk wooed Twitter shareholders with financing details of his offer.

Under pressure, Twitter started negotiating with Musk to buy the company at his proposed $US54.20 per share price.

"Free speech is the bedrock of a functioning democracy, and Twitter is the digital town square where matters vital to the future of humanity are debated," Musk said in a statement.

Former Twitter CEO Jack Dorsey thanked Musk and Twitter CEO Parag Agrawal for "getting the company out of an impossible situation".

"Twitter as a company has always been my sole issue and my biggest regret. It has been owned by Wall Street and the ad model. Taking it back from Wall Street is the correct first step," he tweeted.

Twitter shares rose 5.7 per cent on Monday to close at $US51.70. The deal represents a near 40 per cent premium to the closing price the day before Musk disclosed he had bought a more than nine per cent stake.

Even so, the offer is well below the $US70 range where Twitter was trading last year.

Musk's move continues a tradition of billionaires' buying control of influential media platforms, including Jeff Bezos' 2013 acquisition of the Washington Post.

Twitter said Musk secured $US25.5 billion of debt and margin loan financing and is providing a $US21 billion equity commitment.

Musk, who is worth $US268 billion, according to Forbes, has said he is not primarily concerned with the economics of Twitter, but with having a public platform that is "maximally trusted and broadly inclusive", which is "extremely important to the future of civilisation".

Musk is chief executive of electric car maker Tesla and aerospace company SpaceX, and it is not clear how he much time he will devote to Twitter or what he will do.

"Once the deal closes, we don't know which direction the platform will go," Agrawal told employees on Monday.

Musk's 84 million-strong Twitter account is seen as an important, free public relations and marketing tool for Tesla.

The transaction was approved by Twitter's board and is subject to a shareholder vote.

Although it is only about a 10th of the size of social media platforms such as Facebook, Twitter has been credited with helping spawn the Arab Spring uprising and accused of playing a role in the January 6, 2021, storming of the US Capitol.

After Twitter banned Trump over concerns around incitement of violence following the US Capitol attack by his supporters, Musk tweeted: "A lot of people are going to be super unhappy with West Coast high tech as the de facto arbiter of free speech."

The White House declined to comment on Musk's deal, but said President Joe Biden had long been concerned about the power of social media platforms to spread misinformation.

© RAW 2022

Russia announced a new ceasefire and a humanitarian corridor on for civilians trapped in a steel plant in the besieged Ukrainian port city of Mariupol.

According to the Defence Ministry in Moscow, the Russian army was set to cease hostilities at 2 pm local time on Monday and civilians should then be able to leave the industrial zone via a humanitarian corridor.

The Azovstal steel plant became a last refuge for the people still trapped in Mariupol.

According to Russian sources, about 2,500 Ukrainian fighters and foreign mercenaries are still there. Kiev says there are also 1,000 civilians in the steel plant.

Early on Monday, a series of Russian offensives were blocked in eastern Ukraine, according to reports out of Kiev.

The news comes after a night of secretive meetings between Ukrainian officials and visiting US envoys.

Ukrainian sources also said that five railway stations in central and western Ukraine have been hit by missile strikes.

"Russian forces are systematically destroying the infrastructure of our railyways," the head of the country's railways, Olexandr Kamishin wrote on his Telegram channel.

Reports of missile attacks also emerged from Lviv in the west and Vinnytsia in the south-west of Ukraine.

The reports are impossible to confirm independently.

The civilian death toll amid the Russian invasion stands at 3,818 according to Ukrainian district attorney Iryna Venediktova, in comments reported by the Interfax-Ukraine news agency.

She noted, however, that the statistics are incomplete, as authorities are unable to investigate in many parts of the country due to the ongoing invasion.

Meanwhile, Kiev does not want to remove the goal of joining NATO from its constitution, even though this is one of the main targets of Russia's aggression on its neighbour.

"Amendments to the constitution are not an end in themselves and will not become one," Parliamentary Speaker Ruslan Stefanchuk told the online newspaper Ukrayinska Pravda in an interview published on Monday.

Stefanchuk also stressed that the territorial integrity of the country is a "red line," as Moscow is also demanding Ukraine to officially renounce the Black Sea peninsula of Crimea, which was annexed in 2014, and the eastern Ukrainian regions of Donetsk and Luhansk.

US media reported after the late-night visit on Sunday by US Defence Secretary Lloyd Austin and US Secretary of State Antony Blinken that more high-level diplomatic visits are expected this week. More offers of military aid are apparently expected.

The two men met Ukrainian President Volodymyr Zelensky as well as other high-ranking Cabinet officials. Most details about the visit - even its planning - were kept under tight wraps by the White House.

Blinken said after the visit to Kiev that Russia is coming up short in its attempts to conquer Ukraine.

"When it comes to Russia's war aims, Russia is failing, Ukraine is succeeding," he said.

US President Joe Biden did say that he plans to return the US diplomatic presence to Ukraine.

He nominated Bridget Brink, the current US envoy to Slovakia, to be ambassador to Ukraine. This must now be approved by Congress.

© DPA 2022

Sacrifices made in wars past and present have been remembered at Anzac Day ceremonies across the country and overseas.

The national dawn service in Canberra - marking the 107th anniversary of the Anzac landing at Gallipoli - began with a moment of quiet reflection followed by the sound of a didgeridoo played by Worimi man, Leading Aircraftman Tarryn Roach.

Army veteran Mike Ruffin - who served in Malaya, Borneo and Vietnam - told the service at the Australian War Memorial it was a day to reflect on the Anzac spirit.

He spoke of his personal experience on New Year's Eve in 1968 during the Vietnam War, which had forged a lasting bond between mates.

"In hindsight, it seems inconceivable that five men could run across 100 metres of open ground whilst being subjected to that amount of fire and not receive a single gunshot wound," he said.

"Had any one of us been wounded, that would have been the end as we would never have left a mate behind.

"Every Anzac Day, I reflect on that experience and am so grateful that we all survived. We still keep in touch to this day."

He said Australia was fortunate that current service personnel were "so highly trained, prepared to take the risks and committed to serving their country when asked to do so".

Prime Minister Scott Morrison and Labor deputy leader Richard Marles attended the dawn service in Darwin. Labor leader Anthony Albanese remains in isolation at his Sydney home as he recovers from COVID-19.

Mr Morrison said as Australians honoured their own fallen who fought for liberty and freedom, "we stand with the people of Ukraine, who do the same thing at this very moment".

"Our world is changing. War does strike Europe again. Coercion troubles our region once more and an arc of autocracy is challenging the rules-based order our grandparents secured," he said.

"Democratic, free peoples are standing together again."

Mr Albanese said in a video message the Australian character was confirmed at Gallipoli and since then Australians had "stood steadfast as warriors and as builders and keepers of the peace".

"Yet as the war in Ukraine so tragically reminds us, darkness is not vanquished from the world," he said.

"It reminds us freedom cannot be taken for granted. It reminds us that freedom isn't free."

It is the first Anzac Day since forces withdrew from Afghanistan, where 41 Australians died in service, and large crowds returned as COVID-19 restrictions eased.

This year also marks the 80th anniversary of Anzac Day commemorations at the Australian War Memorial.

Around 20,000 people gathered there for the dawn service and veterans' march, the first time in three years attendance has not been restricted by COVID rules.

Director Matt Anderson said the numbers attending was a powerful reminder of the connection Australians have with Anzac Day.

In his national address, Governor-General David Hurley said the Anzac legacy was not reflected in a single individual or event but was the "sum of thousands of stories".

"Of ordinary Australians who, when given a job to do, got it done, did it in a way that made us proud and looked after each other during and after," he said.

"The characteristics that we take from the Anzac legacy to define us - mateship, endurance, courage and sacrifice - are inherent in Australia."

Delivering an address in Sydney, Major General Matthew Pearse said it was a day to give thanks for all veterans for their service, their sacrifice and their resilience.

"They're filled with stories of ordinary Australians who pulled together despite adversity to support their mates and put their lives on the line to defend our national interests and secure a brighter future."

Overseas, Anzac services took place in Turkey, Thailand, India, Papua New Guinea and France.

© AAP 2022

Australians attending events to commemorate Anzac Day are being urged to take all necessary COVID-19 precautions to protect the vulnerable.

Many jurisdictions are returning to full-scale Anzac Day services after two virus-disrupted years, while most states and territories are in the process of further easing coronavirus restrictions.

However, Victorian health officials have asked patrons to remember their masks when in situations that make it hard to physically distance, particularly in crowds or at indoor environments.

Anyone who has COVID symptoms is being encouraged to stay home and get tested, while people meeting indoors pre- or post-service should open doors and windows to maximise air flow.

"As important as the Anzac Day march and our dawn services are, there may be elderly and vulnerable people there we need to protect," the state's chief health officer, Brett Sutton, said.

Seven-day isolation for close contacts is no longer mandatory in NSW or Victoria as case numbers plateau or dip amid the current Omicron sub-variant wave.

Household contact quarantine rules will be ditched in the ACT after Anzac Day, while Queensland is moving to scrap quarantine for unvaccinated international arrivals by Thursday.

South Australia will also drop the requirement for close contact isolation from April 30 but they must take five rapid antigen tests over seven days.

Masks will also be required outside the home, high-risk settings like aged care centres will be off limits and employers and schools will need proof of status.

Vaccination status and check-in requirements for social and sporting venues are being wound back in Victoria, although mandates for workers in multiple industries have been retained.

NSW is shifting to a risk assessment model, with household contacts of positive cases no longer needing to isolate for seven days, so long as they continue to test negative.

They should still work from home where possible and avoid high-risk settings.

Almost 34,000 new COVID-19 cases were recorded across Australia on Sunday along with 22 deaths, pushing the national toll since the start of the pandemic past 7000.

Some 7004 Australians have lost their lives to coronavirus, with NSW and Victoria accounting for four out of five deaths.

A teenager was among three COVID-related deaths reported in WA on Sunday, as Premier Mark McGowan's child recovers at home with the virus after being released from hospital.

LATEST 24-HOUR COVID-19 DATA:

NSW: 7985 cases, four deaths, 1631 in hospital, 64 in ICU

Victoria: 7643 cases, four deaths, 441 in hospital, 31 in ICU

Northern Territory: 333 cases, 51 in hospital, one in ICU

Queensland: 4639 cases, two deaths, 478 in hospital, 12 in ICU

Tasmania: 867 cases, 43 in hospital, one in ICU

South Australia: 3175 cases, 247 in hospital, 11 in ICU

Western Australia: 5639 cases, one death, 240 in hospital, nine in ICU.

© AAP 2022