Chief Medical Officer Dr Paul Kelly has urged all state and territory chief health officers to mandate masks in all indoor settings, citing rising case numbers for the new COVID-19 variant.

Acting Premier James Merlino says Victoria will take Dr Kelly's advice on board before making a decision on reintroducing compulsory masks in hospitality and entertainment venues.

"Mask wearing is a prudent common-sense measure. It can be inconvenient but it's a small inconvenience for a significant public health benefit," Mr Merlino told reporters on Tuesday.

"There's no restrictions on getting together with loved ones, with family and friends to celebrate Christmas, to celebrate New Year, to enjoy the summer. None of those things are changing."

No change will be made to the unlimited crowd cap for the Boxing Day Test at the MCG, despite fears it could become an Omicron superspreader event.

"The contract with people of Victoria (was) get vaccinated and that means an end to lockdown, it means enjoying events," he said.

Opposition health spokeswoman Georgie Crozier said Victorians wanted surety going into Christmas and had not signed up for greater restrictions.

"The only reason (Victoria would go into further restrictions) is because our health system isn't up to scratch," she said.

In the absence of Premier Daniel Andrews, Mr Merlino will stand-in as the Victorian representative at Wednesday's "informal" virtual meeting of national cabinet, joining other states to call for a shorter COVID-19 vaccine booster interval.

"I want it as short as possible," Mr Merlino said.

No new Omicron cases have been identified in Victoria in the 24 hours to Tuesday, after the state added a further 1245 new COVID-19 infections and six deaths.

Victoria's testing system continues to buckle under the weight of people seeking testing in the lead up to Christmas.

At least 15 testing sites were temporarily closed at 9am after reaching capacity, including the Bourke Street walk-in and Albert Park drive-through.

Queues eased after the morning peak, enabling several sites to reopen.

In response to overwhelming demand, a new testing site opened at Town Hall on Tuesday and will operate until January 24 .

Sites have also been added in Dandenong, Berwick and Frankston, with extended opening hours at others in anticipation of the Christmas rush.

"I am asking for people's patience - I know this has been a very difficult time and it's quite an inconvenience," Mr Merlino said.

"But for the most part, across all of our 260 sites, we're getting through (tests) in 40 minutes on average."

The surging demand, he said, has been fuelled by Victorians needing a negative test result to travel interstate to reunite with friends and family over Christmas.

Australian Associated Press