Victoria has confirmed six more local coronavirus infections, as millions wait anxiously to learn if the state is dealing with yet another COVID outbreak.

Three of Thursday’s cases are linked to existing clusters, and were in quarantine.

Three remain under investigation. They include a woman in her 20s, who is a teacher at Al-Taqwa College in Truganina, in Melbourne’s outer-west.

Her case was revealed on Wednesday afternoon, just hours after the state had posted zero local infections for the first time since a Delta outbreak prompted its fifth lockdown in July.

Victorians had been eyeing virus restrictions being further wound back next week, but the latest cases might put those in jeopardy.

Tweet from @VicGovDH

The teacher’s infection has also prompted the closure of at least four Melbourne schools as state authorities race to trace her movements.

Another one of the mystery cases involves a Newport Football Club player who took the field at Shorten Reserve on Saturday for a senior’s match against West Footscray.

The Western Region Football League said he started to feel unwell this week and did not attend training on Tuesday.

Newport president Marwan Abou-Zeid said the player contacted the club immediately after learning of his positive result on Wednesday.

His teammates and club officials have been told to get tested and isolate until further notice.

“We’ve stopped everything and are just waiting for the health department to get back to us with what tier exposure site the club is in,” he said.

Victorian authorities will provide more details in an update later Thursday.

Al-Taqwa College is one of the schools that has been shut, with more than 2000 students and 300 staff ordered to get tested and self-isolate.

In a statement on Wednesday night, the school said it would be locked down for 14 days and classes conducted online until August 18, unless the health department advised otherwise.

The Ilim College and Australian International Academy campuses, as well as the Islamic College of Melbourne (ICOM) at Tarneit in Melbourne’s west, were also shut on Thursday as a precaution.

In separate letters, the three schools reassured parents that no students or staff had tested positive so far.

“There are many primary contacts at ICOM who may have been in contact with the Al-Taqwa positive confirmed case,” one said.

The Al-Taqwa teacher is isolating and being interviewed by contract tracers and with urgent investigations are underway into how she contracted the virus.

She lives in the Hobsons Bay area with her husband. He was tested on Wednesday night.

Victoria’s COVID-19 testing commander Jeroen Weimar said the woman became symptomatic at the end of last week and might have been infectious in the community for a week before testing positive.

“The 28th, 29th, and 30th [of July] – we’re assuming that’s the point in time when she may have been infectious,” he told ABC Radio on Thursday.

The college has been listed as a tier-one exposure site across those three days, while a Coles at Yarraville is a tier-two site for specific times on July 29.

• See an updated list of Victorian exposure sites here

Mr Weimar said some exposure sites listed in the Hobsons Bay area might be a connection point for the woman’s infection.

Al-Taqwa College was a significant location for transmission in Victoria’s second wave in 2020.

Thursday marks the one-year anniversary of Victoria recording 725 cases, the highest daily number of infections in its deadly second wave of the virus.

-with AAP