Health authorities added to the list of the city’s exposure sites early on Thursday morning, and there are reports of queues forming at suburban test sites.

Victorians must again wear face masks and limit household gatherings after a Melbourne quarantine hotel worker tested positive to COVID-19, possibly contracted from an international tennis player.

The 26-year-old man from Noble Park in the city’s southeast visited numerous public places and shops before returning a positive test on Wednesday.

He had been employed as a “resident support worker” at Melbourne’s Grand Hyatt, where scores of international tennis players have been quarantining after arriving for the Australian Open. He worked his most recent shift last Friday.

Up to 600 Australian Open players and officials reportedly must isolate and undergo testing.

All play was suspended at Melbourne Park on Thursday, with the tournament due to start in four days.

State Opposition Leader Michael O’Brien said the government must make a call in the next couple of days about whether the Open could go ahead.

“We don’t want to see a situation as we did (last year) with the Grand Prix, where crowds were literally turning out to be let in, only to be turned away,” he said.

“The government needs to decide whether it is safe for the Australian Open to proceed.”

O’Brien said questions had to be asked about how the worker contracted the virus.

“This is how it started last year … clearly, something went wrong. And we need to find out what went wrong, how it went wrong. We cannot afford to have history repeat itself,” he said.

Victoria’s Deputy Chief Health Officer Professor Allen Cheng said the risk to players and their support staff was low.

The hotel worker, who was on the same floor as infected guests, worked his last shift on Friday, returning a positive result on Wednesday.

“I think it’s unlikely but we have asked for testing of all of the players and other people who have been in that hotel,” Cheng said on Thursday morning.

“We think the risk to other guests at the hotel, so tennis players and their accompanying staff, is relatively low because they were in the rooms at the time as opposed to staff who were outside the rooms.

“That said, the last case to leave the hotel for the health hotel left on the 22nd so we’re now getting on to close to 14 days since that time.

“So we think that risk is relatively low so we’re testing them to be sure, and it’s precautionary.”

Cheng said it was “unlikely” the Open will be cancelled, but Premier Daniel Andrews warned it was an unfolding situation.

“The tournament proper should not be affected by this, (but) these things can change,” the premier said.

It’s not yet known if the man is carrying a potent offshore variant of the virus.

“Through an abundance of caution, we’re assuming the worst. I think that’s always a smart thing to do,” Premier Daniel Andrews told reporters overnight.

A supermarket and hotel are among six locations that the Department of Health and Human Services added to the exposure sites in early-morning tweets.

A number of hotel quarantine security guards last year contracted COVID-19, sparking Victoria’s second wave of coronavirus, which killed hundreds of people and led to months of lockdown.

Andrews called for calm and urged widespread community testing as he confirmed the latest positive case.

“This is one case. We are all well trained and well schooled in what to do as a state,” he told reporters overnight.

Health authorities are awaiting further genomic test results to confirm the origin of the man’s virus. Those results are expected on Friday.

Close contacts of the man are in isolation and undergoing testing.

In response, Andrews ordered that from Thursday, everyone in Victoria must wear face masks – including in public and private indoor settings – and household gatherings are limited to 15 people.

Plans to allow more workers back to offices have been paused.

“I don’t want to speculate about what the days and weeks to come hold for us,” Andrews said.

Earlier on Wednesday, health authorities confirmed the transmission of a coronavirus case between guests in separate hotel quarantine rooms.

Two separate groups of guests in opposite rooms at Melbourne’s Park Royal Hotel tested positive for the more infectious UK variant of the coronavirus.

It’s possible the transmission could have occurred during a brief door opening as guests collected food.

The hotel’s ventilation system is being reviewed despite an earlier report finding no air was being shared between rooms or into common spaces.

Some 100 hotel quarantine staff members and 37 returned travellers who have completed their 14 days on the impacted floor are now self-isolating at home. None have yet tested positive.