Victoria confirmed just one new local virus infection – and another in hotel quarantine – on Monday as health authorities say it’s still “too early” to tell if the state’s snap lockdown has worked.

The Health Department said Monday’s new case was one reported as “under investigation yesterday [Sunday]”.

Victoria has 21 active coronavirus cases, including 17 linked to the Holiday Inn cluster that plunged the state in a five-day lockdown on Friday night.

There are also 1100 primary close contacts of infected people.

More than 25,000 Victorians were tested for the virus on Sunday.

Premier Daniel Andrews said Monday’s lone case – in a woman who authorities revealed on Sunday had provided several tests with negative and positive results – meant the state was “well-placed”.

But he would not confirm the lockdown would end on Wednesday, as initially planned.

“This is a promising start,” he said.

“We just have to wait … to wait to see how things unfold today [Monday], tomorrow and throughout Wednesday. We will have more to say obviously with the passage of time and more results and as more things become known to us.

“Right now is too early to be definitive about Wednesday evening.”

Tweet from @VicGovDH

The infected woman attended a family function with a COVID-infected hotel quarantine worker on February 6.

She works in a psychiatric unit at The Alfred hospital in inner-Melbourne, and on psychiatric wards at the Northern Hospital in Broadmeadows, which is run by Royal Melbourne Hospital.

The wards have been locked down and contact tracing is underway.

The woman, who is asymptomatic, was tested four times at the weekend, returning both negative and “weak positive” results.

“Given her exposure and the variability of those results, the public health team have taken the most conservative approach and have deemed her a positive case,” Mr Andrews said.

“This has been a very rapid response and one that is filled with an abundance of caution but that is exactly the approach that we ought to take.”

The cluster associated with the Holiday Inn is dominated by the virulent British strain of COVID-19. Photo: AAP

Victoria’s COVID-19 testing commander Jereon Weimar said 150 primary close contacts had been identified across the two hospitals.

The woman and her child, as well as a woman aged in her 50s, contracted the virus after attending a family function on Sydney Road in Coburg on February 6.

Also on Monday, Mr Andrews defended the five-day “circuit breaker” lockdown for all of Victoria as the “right call”. He said health authorities had to work on the “active assumption” that there were more cases than they knew about.

A full list of exposure sites is on the DHHS website.

The Coburg function was attended by 38 people, including a worker from the Holiday Inn quarantine hotel at Melbourne Airport.

Crowds were banned at the Australian Open at the weekend due to the Victorian lockdown. Photo: AAP

Burnet Institute epidemiologist Michael Toole said the function did not appear to be a super-spreading event.

“Those two people at the Coburg site were infected about a week ago, or were exposed a week ago. We haven’t had any other cases outside of close contacts, so that’s looking good,” he told 3AW radio.

Professor Toole said he supported the five-day precautionary lockdown.

“It was shown in Brisbane and Perth that this approach does work,” he said.

“It looks like there hasn’t been extensive spread here.”

Despite the reassuring rate of negative results from Saturday’s tally of 21,475 tests, chief health officer Brett Sutton rejected a suggestion the five-day lockdown was an overreaction.

“This is a high stakes game,” Professor Sutton said.

“We cannot afford to be wrong here.”

Melbourne airport terminals ground to a standstill on Saturday. Photo: AAP

NZ declared a red zone after three new COVID cases

Meanwhile, Aucklanders woke on Monday to a new lockdown, hoping three days of tougher restrictions ordered by Prime Minister Jacinda Ardern would arrest the spread of COVID-19.

Ms Ardern and her cabinet decided on the short lockdown at an emergency meeting on Sunday after the emergence of three virus cases in one south Auckland family.

Under the the alert level three restrictions, 1.6 million Kiwis in New Zealand’s biggest city face bans on non-essential movement until at least midnight on Wednesday.

It is the second snap lockdown for Auckland since the more stringent 51-day nationwide lockdown early in the pandemic that helped NZ eliminate the virus.

Australia has halted quarantine-free travel for New Zealand for a least three days, from Monday.

-with AAP