Deputy Premier Steven Miles said the state’s health authorities are also trying to contact about 1500 travellers who went through a named contact site at Melbourne Airport. The bornder closure will take effect from 1am Saturday.

Premier Daniel Andrews confirmed the state will enter the lockdown at 11.59pm on Friday.

People will only be able to leave their homes to shop for food and essential items, to provide or receive care, exercise, and work and study if they can’t from home.

The 5km limit on travel will also be reimposed, as will the compulsory use of masks both indoors and outdoors.

The Australian Open tennis tournament will continue without crowds.

Andrews said the UK strain of the virus is “so hyper-infectious and moves so fast that it is presenting a very real challenge” for authorities.

The outbreak, connected to the Holiday Inn at Melbourne Airport, has grown to 13 cases, sparking fears the city could again go into lockdown.

Speaking earlier at a CSL facility in Melbourne, Prime Minister Scott Morrison said he had not yet been briefed by the Victorian government.

But he noted hotel quarantine workers have also contracted the virus in Adelaide, Brisbane, Perth and Sydney, sparking short lockdowns in those cities.

“We have dealt with these before, got on top of them before,” Morrison told reporters.

“A proportionate response that enables the (contact) tracers and others, to be able to get on top of it and get the same successful result we have seen in other states – that can and will be achieved here.”

Morrison said he understood Melburnians did not want to endure another long lockdown.

“As other states have demonstrated, you can get on top of this pretty quickly, and I have reason for confidence that they can do the same thing by following that same process,” he said.

Victoria recorded five new COVID-19 cases on Friday, all of which are connected to the Holiday Inn outbreak.

The new cases include a female assistant manager and four close contacts of people who earlier tested positive to COVID-19.

One of the five is believed to have had some contact with Camberwell Grammar School.

“We believe there will be some additional exposure sites emerging from some of these cases,” Victoria’s COVID-19 Testing Commander Jeroen Weimar said on Thursday.

“That work needs to be done over the coming hours.”

The Brunetti cafe in Terminal 4 at Melbourne Airport was listed as an exposure site early Friday morning, after being visited by the case on February 9 between 4.45am and 1.15pm.

Anyone who visited the cafe during that time needs to get a COVID-19 test and isolate for 14 days.

It brings the total number of exposure sites listed on the Health Department’s website to 30.

Weimar said authorities were “right on top” of the outbreak, picking up cases among identified contacts who had tested negative just days earlier.

His “working assumption” is all the cases have been infected with the more transmissible UK variant of COVID-19, complicating the containment job.

“This is by no means over,” Weimar said.

“We are still in the opening quarter of the Holiday Inn outbreak, I’m afraid. We’ve got a lot more work to do.”

Jane Halton, who’s on the board of the federal government’s National COVID-19 Coordination Commission, said while the number of new cases was “worrying” their source had also been identified.

“At the moment we are not seeing reports of any cases that have an unidentified source,” she told Nine’s Today Show.

“I really hope we don’t need to lockdown but everybody right now needs to read that list of what the hotspots are, think about where they have been (and) get themselves tested.”

The cluster has prompted several states to tighten borders to travellers from Greater Melbourne.

South Australia locked out travellers from the Victorian capital at midnight on Thursday, while Queensland will bar entry to visitors of the city’s exposure sites from 1am on Saturday.

Western Australia also announced its hard border to Victoria would be extended for at least another seven days.

An undeclared nebuliser, used inside the room of an infected family of three at the hotel, is the suspected cause of the outbreak.