The extreme heat policy has been implemented at the Australian Open as temperatures soared beyond 42 degrees.
The roof on Hisense Arena and Rod Laver Arena will be closed to allow matches to continue but all matches on outside courts will be halted at the end of the next set.
Officials have declared play will not re-start until at least 2pm WST.
West Australian Casey Dellacqua is yet to play her doubles match with Ash Barty and it has been scheduled for an outside court.
After temperatures consistently above 40 degrees in Melbourne since Tuesday, tournament referee Wayne McKewen opted to enforce the extreme heat rule on Thursday.
The ruling means current matches being played will be suspended at the conclusion of the set and no scheduled matches on outside courts will start until conditions improve.
The announcement will come as a relief to the players, with Australian star Samantha Stosur on Wednesday night urging Open officials to apply some common sense if forecast temperatures of 44 degrees hit Melbourne Park on Thursday.
"If it gets to 44, that is certainly another step up," Stosur said.
"I think players and everybody involved have to be really careful. You've got to do what you can to obviously go out and play as best you can.
"If it's not cooled off, then you've got to really do the right things.
"It's not just for us. It's the fans, the linespeople, the ball kids. Everyone is suffering out there.
"I think there's got to be some common sense, whatever looked at, because you don't want it to get dangerous and have somebody getting hurt because of it."
With a low level of humidity meaning the extreme heat policy wasn't invoked, the tournament's chief medical officer Dr Tim Wood said heat-related issues were down on Tuesday.
"There were only a couple of court calls today related to the heat and no player required medical intervention either during or following their match," he said.