(CNN) -- Searing temperatures in Melbourne have disrupted play at the Australian Open, where tennis players have been struggling in the heat in recent days.

Organizers of the grand slam event said Thursday that they had introduced an "extreme heat policy" after temperatures rose above 40 degrees Celsius (104 degrees Fahrenheit).

That means that matches already under way on court will be suspended at the end of the set being played.

The organizers said the roofs would be closed at the Rod Laver Arena and the Hisense Arena so that players could continue their matches on those courts.

But new matches won't start on outdoor courts "until the temperature falls back down to a temperature deemed fit for play by the tournament director," the statement on the website said.

The severe heat at Melbourne Park this week has already caused problems for players.

Canadian Frank Dancevic fainted during his defeat in the first round on Tuesday. He said he thought the conditions were "inhumane."

On the same day, China's Peng Shuai blamed the heat after she cramped up and vomited during her defeat to Kurumi Nara of Japan.

And it's not just players who have succumbed to the elements. One of the ball boys fainted during 11th-seed Milos Raonic's four-set victory over Spain's Daniel Gimeno-Traver on Tuesday.

Some players worried

Several players have voiced concerns about the conditions.

"Whether it's safe or not, I don't know. You've just got to be very careful these days," Britain's Andy Murray, who has been a finalist in Melbourne in three of the last four years, said Tuesday. "There's been some issues in other sports with, you know, players having heart attacks."

Women's world No. 1 Serena Williams said Wednesday the fear of dehydration was giving her sleepless nights.

But 17-time Grand Slam winner Roger Federer appeared unfazed.

"Just deal with it, because it's the same for both (players)," he said Tuesday after defeating spirited Australian James Duckworth in the first round.

Before Thursday, tournament officials had already introduced heat-related measures for matches in the women's draw, allowing for an extended break between the second and third sets.

The Australian Bureau of Meteorology forecasts maximum temperatures in Melbourne of 44 degrees Celsius (111 degrees Fahrenheit) for Thursday and Friday.

Temperatures are then expected to drop into the low 20s (high 60s and low 70s in degrees Fahrenheit) starting Saturday.

The heat wave currently blasting southern Australia comes after the country experienced its hottest year on record in 2013, according to the Bureau of Meteorology.

CNN's Elizabeth Joseph and Steve Almasy contributed to this report.

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