PHOTOS: Heat stops play at Australian Open

Play on the outer courts at MelbournePark was called to a halt on day four of the Australian Open on Thursday with temperatures hitting 41 degrees Celsius (106 Fahrenheit) and still rising.

Organisers, who had been slammed for forcing players to play on in searing temperatures on Tuesday and Wednesday, enacted the third stage of their "Extreme Heat Policy" for the first time at about 1.50pm local time (0250 GMT).

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"FINALLY!!!! Play suspended because of the heat... Heat policy should have been in 2 days ago already.. #burning #crazy #nothealthy," tweeted Belgian player Kirsten Flipkens.

Play would not resume until conditions had eased and definitely not before 5pm (0600 GMT), organisers said.

The exception would be on the Rod Laver Arena and Hisense Arena show courts, where play would continue after the retractable roofs were closed.

With players having to finish the ongoing set before play ceased or the roofs were closed, Maria Sharapova's match on Rod Laver Arena continued in the full glare of the sun for 50 minutes after the Extreme Heat Policy was enacted.

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The third seed eventually finished off Italian Karin Knapp 6-3, 4-6, 10-8 to reach the third round.

"They should cancel the matches at this heat. What they did but still some matches are on, not fair," tweeted her fellow Russian Svetlana Kuznetsova.

"I remember they stop my match here in the middle of the set so it means it can be done..i know that out sport is (tough) but not like that.."

With forecast highs of 44 degrees Celsius, a third straight day of suffocating heat at the year's first Grand Slam was guaranteed to keep the debate on whether play should continue rumbling on.

On Tuesday, when temperatures peaked at 42.2 degrees, Canadian Frank Dancevic passed out during his first round match and accused organisers of forcing players to play in "inhumane" conditions.

Ivan Dodig became the 10th player to retire in the first three days of the tournament on Wednesday and said he feared for his life after being rendered immobile by the heat on the exposed outer courts.

Under a change to the rules for this year, the decision on whether to stop matches at the tournament is now at the discretion of tournament director Wayne McKewen.

Rather than use the raw Celsius readings to assess the heat, organisers prefer to use the Wet Bulb Global Temperature composite, which also gauges humidity and wind to identify the perceived conditions.

McKewen said that the threshold was not reached on Tuesday and Wednesday with world number seven Tomas Berdych suggesting that perhaps it had been set too high.

The hot weather is forecast to continue through Friday before a dramatic drop in temperatures at the weekend.