VICTORIA will enter its fifth lockdown in an effort to contain a growing outbreak of the COVID-19 Delta variant in the state.

NSW COVID cases: Latest case numbers, July 15, 2021

Premier Daniel Andrews said Thursday afternoon the state-wide lockdown, which will begin at 11.59pm Thursday and continue until 11.59pm Tuesday night, would be identical to that of the state's last hard lockdown.

"If you were authorised to work then, you are authorised to work now. If you were closed then, you will be closed now," Mr Andrews said.

Victoria recorded two further cases on Thursday taking the state's total to 18, with 1500 primary close contacts identified, and a further 5000 secondary close contacts, the Premier said.

"This will be a hard lockdown, identical to what we did a couple of weeks ago," Mr Andrews said. "We are doing it the way that we always do it.

"We have a list of those people who can work, a list of those businesses that can be open, and a list who cannot. So it is essentially a repeat of the successful strategy from a couple of weeks ago.

"That was successful then. This will be successful now."

"This is so infectious - this is such a challenge - that we must do this."

Mr Andrews said he empathised with residents of the state's regions, who will enter lockdown alongside the city, but said the measures were necessary to bring the outbreak under control.

"I know and understand how frustrating it is for communities that don't have case and exposure sites, to be lockdown. We will release those parts of Victoria before next Tuesday if it is safe to do so," Mr Andrews said.

"It's very challenging to be lockdown because of things that are happening in Melbourne. The challenge here is that they may be happening in other places. We don't know yet and we have to have an abundance of caution."

The Premier also foreshadowed announcements for business support as early as Friday.

In NSW, meanwhile, COVID cases have begun to stabilise but Premier Gladys Berejiklian warns she "won't hesitate to make difficult decisions if she has to" unless case numbers start dropping.

EARLIER:

The two cases are in addition to 10 locally acquired infections recorded in the 24 hours to Thursday morning, all of which were previously reported.

COVID-19 Commander Jeroen Weimar said the cases appear to be linked to an infectious Maribyrnong man who attended the match and was seated the MCC member's reserve on level 2.

But he said the duo were not known contacts of the infected man and it appeared to be a case of "stranger-to-stranger transmission".

"They were sitting in very different parts of the ground. There's no obvious relationship between them. The interviews and discussions are ongoing," Mr Weimar told reporters.

The infected man, aged in his 60s, attended the game with his friend, a teacher from Bacchus Marsh Grammar school who lives in Barwon Heads.

The teacher and two of his family members, a nine-year-old child and a man in his 60s, have also subsequently tested positive for COVID-19.

Both Bacchus Marsh Grammar and Barwon Heads Primary School have been closed and more than 3500 students and staff are self-isolating.

The child who tested positive on Thursday is understood to have attended St Patrick's Primary School in Murrumbeena, which has also closed.

The Maribyrnong man lives at the Ariele Apartments complex, where removalists from NSW, who have since tested positive to COVID-19, were working on July 8.

Another chain of community transmission occurred at Craigieburn Coles on Saturday, when a man contracted the virus after speaking to a member of a family that had recently returned from NSW.

The family of four have all progressively tested positive since Sunday. They live in the local government area of Hume and were granted a red zone permit to return from NSW.

Mr Weimar said there were 16 active COVID-19 cases connected to the two chains of transmission and more than 75 exposure sites.

Some 1500 primary close contacts and 5000 secondary contacts are self-isolating.

"This is probably the fastest response we have ever seen to an outbreak that's moving more quickly than we have ever seen in Victoria, or I suspect anywhere else in Australia," Mr Weimar said.

Meanwhile, it was announced late on Wednesday that anyone aged over 12 will be required to wear a mask in all indoor settings, unless an exception applies.

Masks must also be worn outdoors when social distancing isn't possible.

Victorian locations where there is a risk you may have been exposed to COVID-19: https://www.coronavirus.vic.gov.au/exposure-sites

- with reporting by Benita Kolovos and Callum Godde, AAP

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