One of Melbourne's biggest hospitals has been forced to send staff home and limit access to its cancer ward, as it investigates a deadly cluster of COVID-19 cases in inpatients.

Key points: The Alfred has limited access to its haematology and oncology ward after inpatients and staff were diagnosed with the virus

The Alfred has limited access to its haematology and oncology ward after inpatients and staff were diagnosed with the virus It comes as Victoria's tally of suspected cases of community transmission rose from nine to 16

It comes as Victoria's tally of suspected cases of community transmission rose from nine to 16 The state's confirmed coronavirus cases have risen by 54 across the state to a total of 574

In a statement, The Alfred said four inpatients at its haematology and oncology ward had tested positive to the virus, two of whom died.

Three ward staff have since tested positive to the virus and an unspecified number of staff have been sent into self-isolation.

The hospital said contact tracing had not yet identified the source of the infections and it was carrying out a full investigation.

Access to the affected ward had been "limited" as a result, the statement said.

Alfred Health chief executive Andrew Way said the situation was upsetting for everyone involved.

"This situation highlights how devastating the virus can be for vulnerable patients," he said.

"I urge the community to follow health advice and to self-isolate if they're unwell. We need to act now to protect those at risk in our community."

On Wednesday, it was revealed that four workers at Werribee Mercy Hospital in Melbourne's west had been diagnosed with COVID-19.

Warning of 'snowballing effect' if hospitals become overwhelmed

Brendan Crabb, the CEO of the medical research organisation The Burnet Institute, said the tragic deaths and the staff infections were "a big warning sign".

"They [staff] are really in the literal firing line. It's a very dangerous place for health workers to be," Professor Crabb told ABC Radio's Statewide Drive.

"If their services get overwhelmed we're going to see a lot of damage done to our health workers, not just to the broader community. And of course that has a snowballing effect."

Fears the state's hospitals could be overrun at the height of the pandemic have led to suggestions major buildings like the Melbourne Convention and Exhibition Centre could be repurposed as medical facilities.

Premier Daniel Andrews said the Government was looking at "all manner of different settings", including the already-announced recommissioning of parts of the former Peter MacCallum cancer hospital and Baxter House at Geelong, which will be converted into a public hospital.

It has been suggested the Melbourne Exhibition and Convention Centre could become a place to treat COVID-19 patients if hospitals are overwhelmed. ( ABC News: Patrick Rocca )

"It makes sense to look at all the different options, whether it's the convention centre, Jeff's Shed, the Exhibition Buildings, there's many different settings," he said.

"I'd certainly hope that we can be successful, we can all play our part, and we don't need a space as big as that to care for anybody because we've flattened the curve because we've all stayed at home."

The Great Hall of the Royal Exhibition Building in Carlton was converted into a hospital during the influenza pandemic in 1919. ( Supplied: Museums Victoria )

Victorians told if they flout restrictions 'you will be killing people'

Throughout his press conference on Friday afternoon, Mr Andrews implored Victorians not to leave their homes unless necessary these school holidays.

"Anyone who is not following the rules is being selfish, but it's more than just behaving badly, you will be killing people," he said.

"I can't be clearer than that. Do the right thing for yourself, do the right thing for those who are vulnerable, do the right thing for people who are otherwise healthy."

Victorian families are being urged not to spend the upcoming school holidays outside. ( ABC News: Stephanie Ferrier )

Five thousand rooms from hotels and other accommodation providers will used to quarantine overseas travellers returning to the state from midnight on Saturday.

The move came after Prime Minister Scott Morrison announced that from midnight on Saturday, all passengers who arrived in Australia would go into mandatory quarantine in hotels.

Concerns had been raised about some people not following self-isolation requirements, particularly after getting off cruise ships.

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Mr Andrews said keeping travellers in one location would help reduce the spread of the virus throughout the community.

"[These] continued, next big steps are exactly what we need if we are going to contain this virus, save lives and make sure that our health system doesn't get overrun," he said.

"[Returning travellers] will be housed, they will be fed, they will be transported. There will be no cost to them.

"This is the best way to ensure absolute compliance."

Monitoring would carried out by Victoria Police, health authorities and the Australian Defence Force, the Premier added.

Melbourne's inner-city beaches closed

Mr Andrews called on all Victorians to avoid unnecessary social contact and stay home, and warned he would extend shutdown measures if necessary.

"No one should be at the beach, and if I have to take action to prevent people from going to the beach, I will. I hope it doesn't get to that," he said.

"If you choose to be at the beach that is a choice that may cost someone their life."

Police moved in to tell people to leave the beach hours after the Premier threatened to have them closed. ( ABC News )

Hundreds of people on the beach, the foreshore and walking paths ignored his pleas, crowding onto St Kilda Beach in the warm autumn sunshine.

At 6:00pm, the City of Port Phillip acted, closing all of its bayside beaches from Elwood to Port Melbourne, including St Kilda Beach.

The St Kilda Botanical Gardens are also closed.

"So people will not be able to go on the beach and sunbake or sit on the sand," Mayor Bernadene Voss told ABC Radio Melbourne.

"Unfortunately we've had to make this decision because it's very clear people are not listening to what the Premier has said and people need to stay home."

She said the detail was still being worked out but that the council was also discouraging people from jogging along the beachfront or swimming in the bay.

Some people gathered at St Kilda Beach, in defiance of the call for Victorians to stay at home. ( ABC News )

"I very much understand that people need to get out and get some fresh air after being cooped up inside all day, all of our other parks are open … if people continue to flout the rules and continue to congregate, we'll actually take further measures to stop COVID-19 and protect our community," Cr Voss said.

She said police would be enforcing the beach bans.

Rising community transmission a 'serious concern'

The State Government on Friday morning reported the number of Victorian cases had risen by 54 across the state to a total of 574, while the number of suspected community transmissions nearly doubled from nine to 16.

The state's death toll remained at three on Friday morning, including the two deaths at The Alfred. All three men were in their 70s.

At a national press conference on Friday, Chief Medical Officer Brendan Murphy emphasised that the rate of community transmission was the "single most important" measure of the pandemic's spread.

Community transmissions are when people contract the virus, but health authorities are unable to trace the spread of the disease back to someone who has arrived in Australia from overseas.

"We're not kidding ourselves — if community transmission becomes significant, that is the real serious concern," he said.

A Melbourne bakery temporarily shuts down as part of efforts to curb the spread of COVID-19. ( ABC News: Ron Ekkel )

Earlier this month, the state's Chief Health Officer Brett Sutton said he would be closely following the spread of "community transmissions" to decide what social-distancing measures were required.

"When we see a lot of community transmission, maybe the majority of cases are community transmission, that is a real time to reflect on the fact that your identification, isolation and quarantining measures are not going to hold it," he said earlier this month.

Professor Sutton, who has been an advocate for tougher interventions in response to the pandemic, said that would be a sign of an uptick of an epidemic curve and social distancing would become the critical measure to limit the spread of the disease.

Unions, business chamber call for wage subsidies

The Victorian Trades Hall Council and the Victorian Chamber of Commerce and Industry on Friday issued a joint call for the Federal Government to subsidise workers' wages.

Luke Hilakari, secretary of Victorian Trades Hall Council, said the current situation was untenable.

"The welfare system is ill-equipped to deal with what's going on right now. What we're calling for is an 80 per cent wage subsidy, just like Boris Johnson announced in the UK," he said.

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Give socialites 'benefit of the doubt'

The City of Stonnington, which takes in suburbs including Kooyong, South Yarra and Toorak, has emerged as the state's most serious COVID-19 hotspot.

Mayor of Stonnington Steve Stefanopoulos told ABC Radio Melbourne he was surprised by the figures that showed his city had 58 cases and called on all Australians to "just stay home".

Responding to newspaper reports that a cluster of cases had been infected during a social event in Toorak, Cr Stefanopoulos said those responsible should be the "given benefit of the doubt".

"Maybe they didn't know they were infected at the time [and we should give them] the benefit of the doubt," he said.

"But now that we all know this is happening, we need to stay at home and not have these dinner parties and gatherings and [maintain] that social distancing."

Cr Stefanopoulos said he was shocked that some people were still behaving as if there was no pandemic.

"The city is much quieter but people are still shopping in high streets," he said.

"Not just grocery shopping, which is fine, but actually strolling the streets as if nothing was happening.

"Go home, stay home and look after your families."

Cr Stefanopoulos said the city council had closed its public facilities and offered use of the Prahran Town Hall to the Alfred Hospital and Star Health for use as a testing facility.

"It's there for them to use whenever they like," he said.

Food courts can now only serve takeaway after stage two restrictions came into force in Victoria on Wednesday. ( ABC News: Ron Ekkel )

Historic site closures extend

More of Victoria's major historical sites have been closed to comply with restrictions on public gatherings.

Sites including Point Nepean, Werribee Mansion, Hanging Rock, Buchan Caves and the Mount Buffalo Chalet were closed on Friday until further notice.

Parks Victoria CEO Matthew Jackson said the closures were made at the advice of Victoria's Chief Health Officer and were in place to "protect visitors, volunteers, customers and our staff".

The move follows last week's closure of the Twelve Apostles, the penguin viewing platform at St Kilda Pier and several other popular sites due to coronavirus.