Victorian Chief Health Officer Brett Sutton has slammed the "really crap" behaviour of some Victorians, warning that without change Australia is on its way to "thousands of deaths" due to the coronavirus pandemic.

Key points: The total number of positive coronavirus cases in Victoria rose by 111 to 685 on Saturday

The total number of positive coronavirus cases in Victoria rose by 111 to 685 on Saturday It was the state's biggest overnight increase in infections so far

It was the state's biggest overnight increase in infections so far Coastal councils have joined the City of Port Phillip in closing all beaches in the local government area.

On Saturday, the State Government announced new on-the-spot fines for those who breached physical-distancing rules designed to stop the spread of coronavirus.

Councils up and down the coast also brought in bans and restrictions on beaches as people continued to ignore requests not to congregate in groups.

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In some of the strongest language seen from Australian health authorities so far, Professor Sutton issued a stark warning yesterday afternoon.

"Some of the behaviour today — when we're asking people to stay home — has been really crap," Professor Sutton said on Twitter.

"It's hard to change habits and it's hard to see dangers that aren't apparent yet.

"But with 3,000 cases of COVID in Australia this week, we're headed to 100,000 in two to three weeks without change.

"That means thousands of deaths. Overwhelmed health services. Medical staff at unacceptable risk. Unstoppable spread.

"Do the right thing now and #StayAtHome. Today. Tomorrow. Until we're through this, please."

Big fines for breaching social distancing rules

At a press conference on Saturday morning, Police Minister Lisa Neville said individuals would face fines of up to $1,652 for gathering in groups and businesses would cop penalties of $9,913.

Ms Neville said the fines would apply where people were flouting a directive from the Chief Health Officer "such as mass gatherings, 14 days of self-quarantine, weddings and funerals".

The limit on weddings is five people and funerals are capped at 10 people. People can also be fined for organising the auction of a residential property.

People would not be fined for standing less than 1.5 metres apart.

Police told people gathered at St Kilda beach to leave on Friday afternoon after Port Phillip Council closed the beach. ( ABC News )

Premier Daniel Andrews said he hoped no one would be fined but said "giving police these sorts of powers was very important".

"If you are flouting [the] rules, you will be punished," he said.

The number of people diagnosed with coronavirus in Victoria jumped by 111 cases overnight Friday, taking the state total to 685 on Saturday.

Ms Neville said it was the "biggest overnight increase in infection" in Victoria.

"It is still the case that the vast majority of cases, 90-plus per cent of new cases, are either people who have travelled overseas or been in close contact of those who've travelled overseas," he said.

Access to beaches closed or restricted

Beaches in Hobsons Bay and Bayside and along the Mornington Peninsula were closed yesterday until further notice.

Mornington Peninsula Shire Mayor Sam Hearn said the Premiers' comments about not congregating on beaches "were unequivocal" and the shire's beaches would close immediately.

Police are patrolling Williamstown beach to make sure groups of people stay away. ( Supplied )

Signs will inform people of the closures and the beaches will be monitored to ensure people stay away.

A sign on Williamstown Beach on Saturday said the beach was closed and the ABC has been told police are patrolling the area.

A statement from Bayside City Council said the area's beaches had been closed to the public to help mitigate the spread of COVID-19.

"This weekend, council officers will be deployed along the foreshore to inform residents of the beach closure and make sure people are not congregating on the beach," the statement said.

Bass Coast Shire chief executive Ali Wastie also announced yesterday that the area's beaches were closed, but people were still allowed to people to surf, swim, run or walk as long as they did not congregate in groups.

"The closure is to minimise the locations being used as a gathering place during the COVID-19 crisis," Ms Wastie said.

Bass Coast Shire skate parks and playgrounds were closed Friday.

The City of Port Phillip restricted access to all its beaches Friday after crowds congregated against social distancing rules.

Police visiting beaches to break up groups

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At Saturday's press conference, Ms Neville said more than 2,600 checks had been carried out by Victoria Police to make sure people were complying with self-quarantine rules.

She said police would visit Victorian beaches over the weekend to make sure people were complying with social distancing rules.

While councils were deciding on their own to close beaches, Ms Neville said the Government would "quickly close beaches" if large numbers of people continued to congregate at them.

"We don't want to close beaches but if we have to, we will," she said.

Mr Andrews clarified that a "walk at the beach is okay" but said people should not be spending the day at the beach.

"This is no ordinary autumn day," he said.

He reiterated that the measures being taken were not to bring the number of cases of coronavirus in Victoria to zero, but to slow the rate of infection so hospitals could cope.

Mr Andrews said Victoria was not at the stage where public transport timetables needed to be reduced and confirmed there were no changes being made to the construction industry.

"It's not the time to do that. It's time to remind everybody there are rules in place and advice about washing your hands and cleaning equipment," he said.

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Hotel rooms prepared for 14-day quarantine

Mr Andrews said 2,800 hotel rooms were ready to take passengers from flights arriving into Melbourne after Prime Minister Scott Morrison announced all people who arrive in Australia after midnight Saturday would go into mandatory quarantine for 14 days.

Mr Andrews said 26,000 rooms had been offered by hotels across the state.

The government would use Sky Bus buses to move passengers to the hotels.

Mr Andrews said no one on board two cruise ships that docked in Melbourne early Saturday morning would be disembarking.

"No one's getting off those ships. No chance. No one's getting off," he said.

Small businesses to access $10,000 grants

During the press conference, Treasurer Tim Pallas announced that small businesses with payrolls of below $650,000 would be able to apply for grants of $10,000 from Monday.

Mr Pallas said 30,000 of the grants would be available for businesses such as cafes, bars, restaurants, live music venues and other small businesses not able to access the previously announced payroll refunds.

He said $52 million in payroll tax refunds had already been paid to 2,700 small businesses with all eligible businesses who had provided their bank details to receive refunds by the end of next week.

Darebin City Council in Melbourne's north is also lending a helping hand and has announced a $10 million Local Business Resilience and Recovery Package for struggling businesses and community groups.

Mayor Susan Rennie said the package would focus on the most vulnerable in the community "including those at risk of experiencing homelessness, domestic violence, and people from diverse backgrounds, Aboriginal community members and older people living alone without support".

Short term funding, food vouchers, essential supply hampers and pre-made meals will be provided to local family violence, elder abuse, homelessness, and emergency relief services.

National Cabinet will meet again this afternoon.