Play was suspended on uncovered courts at the Australian Open on Thursday as the temperature exceeded 40C for a third consecutive day.
At 13:53 local time (02:53 GMT) and with the temperature at 41C, the "extreme heat policy" was implemented.
Feeling the heat
Maria Sharapova
Take a look at our gallery to see how the heat is affecting the Australian Open
It signalled an end to play on outside courts and the roofs brought across on Rod Laver Arena and Hisense Arena at the end of any active set.
Officials said suspended matches would not resume until 17:00 (06:00 GMT).
"For outside courts new matches will not be called until the temperature falls back down to one deemed fit for play by the tournament director," organisers said in a statement.
Maria Sharapova spent three hours and 28 minutes in the brutal conditions as she battled past Italy's Karin Knapp, in three sets and later questioned the communication between officials and players.
"We have never received any emails or warnings about the weather or what to do," said the Russian.
"Actually, I did receive one, I think, while I was in the ice bath a few minutes ago, and I was like, 'that's a little too late'."
The temperature reached a peak of 42.2C on Tuesday and 41.5C on Wednesday, but the forecast was for a high of 44C on Thursday and when play began at 11:00 local time (00:00 GMT) it was already 38C.
The decision to implement the extreme heat policy is at the discretion of tournament referee Wayne McKewen, who uses the Wet Bulb Globe Temperature reading, which takes into account humidity and wind direction as well as heat.
McKewen had been criticised for failing to suspend play on the previous two days.
After the decision was taken, Belgian player Kirsten Flipkens tweeted: "FINALLY!!!! Play suspended because of the heat... Heat policy should have been in two days ago already.. #burning #crazy #nothealthy."
Russian Elena Vesnina added: "Impossible to play in this heat... it's only about surviving. Forget about beauty of the tennis!"
Alize Cornet of France cries between games while trying to deal with the extreme heat
France's Alize Cornet was reduced to tears during a break in her match against Camila Giorgi
On Wednesday Croatian Ivan Dodig said he feared he "could maybe even die" because of the heat, while a day earlier Canada's Frank Dancevic required medical attention after fainting in his first-round match and said it was "inhumane" to allow players to compete in such testing conditions.
By 14:30 (03:30 GMT) on Thursday the temperature had risen to 43C, with some matches, including Sharapova's marathon contest with Knapp, still in progress.
Sharapova wrapped herself in ice towels between points on Rod Laver Arena, while France's 25th seed Alize Cornet looked in distress on Margaret Court Arena.
"I went further than my limits,'' said a tearful Cornet after beating Camila Giorgi. "It was really hot, that's why I'm so emotional. Doing something physical in this heat is just unbelievable. Even for you guys [in the crowd] sitting in the sun must be terrible.''
American Varvara Lepchenko was among the first players to suffer and she required a medical timeout to have ice rubbed onto her legs after losing five straight games on Court Eight.
On the resumption she won just one more as she lost 4-6 6-0 6-1 to Simona Halep.
"I think they definitely should have just not started the matches in the first place," said Lepchenko.
"And the same goes for a couple of days ago when I played my [first-round] match. It was just the hottest time of the day and I got caught up in that.
"Somehow I survived, but today it just didn't work, and I think they should have started matches after the temperature cooled down a little bit, because this is just too much."
She added: "Obviously it's very dangerous if someone has some sort of conditions with their heart. Being in this temperature is almost like going into a sauna - it's not good."
The timing of Andy Murray's second-round match, due to begin at around 09:30 GMT, should not be affected as he will be on the main Rod Laver Arena.
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