SYDNEY - Play has been suspended at two Australian Open lead-up events after a hotel quarantine worker tested positive for COVID-19, prompting state officials to reintroduce virus restrictions.

No matches were played on Thursday in the Melbourne Summer Series and ATP Cup, while up to 600 players and staff were required to isolate until they returned a negative test result.

Several locations across the city of Melbourne were named as potential transmission sites with authorities acting on the assumption that other people had been infected.

Victorian State Premier Daniel Andrews reintroduced the mandatory use of face masks indoors and reduced the number of visitors allowed in private homes as well as postponing a push to get more workers back into offices.

The positive case was a resident support officer at one of the Australian Open quarantine hotels, and reportedly tested negative for the disease after working on January 29, before later developing symptoms.

It was not known exactly how the man contracted the infection or whether it was one of the more contagious strains being reported overseas, with health officials awaiting genomic sequencing data.

"There's a number of, about 500 or 600 people, that are either players and officials and others who are casual contacts. They will be isolating until they get a negative test," Andrews said.

Andrews added that the Australian Open, scheduled to begin on Monday, would go ahead as planned and that Victoria's health experts and officials as well as the public were experienced in containing such outbreaks.

"We've got one case. We're going to work very hard to keep numbers as low as we possibly can. Decisions have been made, and we'll proceed as we can," Andrews said.

An update on the match schedule for Friday will be announced later on Thursday.