The state recorded 21,966 new COVID-19 cases and 15 deaths on Thursday, with 11,693 of the infections from PCR tests and 10,273 from RATs.

Premier Daniel Andrews announced the state government will order 166 million RATs, in addition to the 44 million tests procured this month.

"It's very important that we keep adding to that stockpile," he told reporters in Melbourne.

"This is a very significant order that we've placed, among the largest, I expect, across the country."

How the tests will be distributed is yet to be announced.

Mr Andrews said the additional tests will cost "hundreds of millions" but declined to give an exact amount as negotiations are ongoing.

He warned the order would take "some time" to arrive as most of the RATs will come from China.

"We're also working on whether we can manufacture and boost some local manufacturing that's already occurring," he said.

Out of the 44 million already ordered, 7.5 million RATs have arrived since Sunday, with more than two million distributed to health workers, staff in sensitive settings, and vulnerable communities. About 750,000 tests have also been handed out at state testing centres.

However, Mr Andrews said some tests did not arrive as planned this week due to the ash cloud from the underwater volcano eruption in Tonga.

Opposition Leader Matthew Guy described the latest order as "too late", noting the coalition first raised the importance of rapid antigen tests back in August.

"The government made a bulk order purchase on Christmas Eve, some months after other states did," he said.

"Now, the premier rolls out today and boasts that he's ordered hundreds of millions of them. Well, it's too late."

Victoria is now managing 246,894 active cases, which includes 1206 people in hospital, an increase of 33 on Wednesday's figures.

The number of people in intensive care sits at 122 and there are 40 people on ventilation.

COVID-19 Commander Jeroen Weimar said the number of health staff unable to work due to becoming close contacts or contracting the virus was beginning to decline.

"Today we have 3900 health staff who are unable to work, that number is pleasingly starting to come down - it was 4500 yesterday," he said.

Victoria activated a system-wide emergency alert for its Melbourne and major regional hospitals on Wednesday to help cope with the pandemic pressures.

Mr Weimar said case numbers were beginning to stabilise, as were PCR testing wait times, which had fallen to half an hour on average.

He said 86.5 per cent of COVID-19 test results were being returned the following day.

Victoria's booster rate has risen to 27 per cent after the government slashed the interval to three months at its state-run clinics on Wednesday.

Mr Andrews had flagged national cabinet could agree on Thursday that three doses of the vaccine are needed to be considered fully inoculated. However, that agreement was not made.

After the national cabinet meeting, Prime Minister Scott Morrison said that would be left to expert advice.

"Whether it be a third dose or a booster, you continue to see people turning up and getting it and that's the outcome you want, whether it be formally a three dose program or a two dose with a booster, I would leave it to the medical experts to advise us," he said.

Mr Andrews said on Wednesday the third dose could soon become mandatory in Victoria, noting a requirement imposed for several essential industries last week.

More than 200,000 booster appointments are available over the next two weeks, with 60,000 additional slots available as part of a four-day 'booster blitz' from Friday at eight state-run hubs.

Australian Associated Press