MELBOURNE (AFP) - Tennis action resumed at Melbourne Park on Friday (Feb 5) after almost all players and officials who had to be tested for Covid-19 received their results, which were negative.

Preparations for the Australian Open were thrown into disarray when a worker at one of the hotels used during their mandatory 14 days quarantine on arrival in Australia became infected with the virus.

More than 500 players and officials were ordered to be tested and isolate until they received their result, with six warm-up tournaments for the opening Grand Slam of the year postponed on Thursday.

But Australian Open boss Craig Tiley said of the 507 people ordered to be tested, the results for 495 had come back and were all negative. Twelve results were pending.

"So far, everyone is negative," he told Melbourne radio station 3AW, adding that he was confident fans would still be able to watch this week and at the Australian Open, which starts on Monday.

"Spectators will continue to be allowed in the site, and we are still selling tickets.

"The site will be an extremely safe place. There's health checks, contract tracing set up, divided into zones, physical distancing."

Play began an hour early with WTA clashes reduced to two sets and a super tiebreaker instead of their usual three sets to ensure as many matches take place as possible.

World No. 1 Ashleigh Barty was one of those in early action, moving closer to a semi-final showdown with Serena Williams after a tough win over Shelby Rogers.

The Australian has yet to rediscover her best after a long layoff but prevailed 7-5, 2-6, 10-4 in 92 minutes in the quarter-finals of the Yarra Valley Classic.

"I thought I did well to hang in there," she said. "There were some challenges but happy to click into gear and find a way."

Novak Djokovic and Naomi Osaka are among the other stars in action.