The federal government has declared Sydney’s northern beaches a national coronavirus hotspot – the first time it has made such a declaration during the pandemic.

The move came as the outbreak in the area grew to 28 cases, including one in Queensland, and Premier Gladys Berejiklian warned residents more virus rules could be imposed if the cluster wasn’t contained.

The number of alerts for Sydney venues continued to spiral on Friday as authorities tried to quell the worrying cluster that emerged only two days ago.

Among the latest venues of concern is the Cronulla RSL, nearly 70 kilometres south of the Avalon club that is at the heart of the outbreak.

Patrons who visited on the Cronulla RSL night of December 16 are among hundreds of thousands of people across Sydney who have been told to get a COVID test and isolate until they are contacted.

The national hotspot declaration will allow the region to get extra support for personal protective equipment, contact tracing and resources for aged care facilities.

Federal Health Minister Greg Hunt said Australia was prepared for the Avalon outbreak but the next few days would be critical as authorities grappled with it.

“We’ve prepared for this moment,” he said.

“We’ve always said that while we’re doing extraordinarily well, there would be outbreaks, there will be circumstances where local clusters emerge and we thank the northern beaches population for their action.

“The next few days will be critical and the behaviour of individuals will be fundamental.”

Prime Minister Scott Morrison has urged people to remain calm and follow advice from local health authorities.

“We have dealt with this before, we’ll deal with it again,” he said on Friday.

NSW authorities have linked the northern beaches cluster to a strain of the virus from the US, but don’t yet know how the illness spread into the community.

Residents in the Northern Beaches cluster area – about 250,000 people – have been told to stay home and get tested if they have any virus symptoms.

Late on Friday afternoon, the Northern Beaches Council said it would close 21 beaches in the area until at least Monday. Elsewhere, there were the now familiar reports of supermarket shelves being stripped of essentials such as toilet paper.

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“I stress to everybody in and around Avalon and the Northern Beaches that for the next three days you shouldn’t leave your home unless absolutely necessary,” Ms Berejiklian said.

“If we get on top of this in the next two or three days, all of us will be able to have a better Christmas.

“If we don’t get on top of it, it could mean further restrictions down the track.”

She also urged Sydney residents to wear masks in places where there was high foot traffic.

“Nobody should be getting on public transport without wearing a mask, nobody in greater Sydney should be going to a supermarket or a place of worship without wearing a mask,” she said.

“It would just be crazy.”

Also late on Friday afternoon, NSW Health issued NSW Health a “strong advisory” for everyone in the area to wear a mask at all times inside. The advice lasts for 72 hours, but the authority stopped short of making masks mandatory.

No other cases have been recorded in relation to a man in Sydney’s south, who worked as a driver shuttling international airline staff to and from Sydney Airport.

But from Tuesday, all international air crew arriving in Sydney will be held at quarantine hotels until their flights out of the country, typically within 72 hours.

Ms Berejiklian said NSW police would take over ensuring crew complied with requirements.

It also emerged on Friday afternoon that several air crew from South America had been penalised for breaching isolation rules.

Other states react

NSW residents face a host of hastily imposed restrictions on their travel to other parts of Australia after the outbreak emerged.

Many of the states have ignored the federal government’s pleas not to make rash decisions about closing borders, with Christmas around the corner.

On Friday, Victoria, Western Australia, Queensland and ACT leaders all urged their residents not to travel to Sydney.

Victorians were told they might face 14 days quarantine should they do so and want to return.

From midnight, a permit system will be in place for NSW residents entering Victoria.

Western Australia has reintroduced a 14-day quarantine requirement for all NSW travellers, while anyone who has entered the state from NSW since December 11 also has to self-isolate.

WA Premier Mark McGowan said the NSW situation was fluid – and being monitored closely.

“If the numbers grow as they have, or even more, then there may well be a requirement to go to a harder border arrangement,” he said.

“That may well be today or tomorrow or the next day. We’ll just wait and see.”

In Queensland, anyone arriving from Sydney’s Northern Beaches after 1am on Saturday will face mandatory hotel quarantine for 14 days.

Tasmania, the Northern Territory and the ACT have also imposed restrictions on people from the Sydney hotspot.

-with AAP