Players fainted and vomited and a ball boy collapsed as the Australian Open boiled in one of the hottest days in its history on Tuesday, prompting Britain's Andy Murray to warn organisers they were risking a tragedy.
The Wimbledon champion queried if it was safe to play in 40 degrees Celsius heat and said the sight of players and ball boys breaking down "looks terrible for the whole sport".
"Whether it's safe or not, I don't know. You just got to be very careful these days," said the world No 4 after his first-round win against Japan's Go Soeda. "There's been some issues in other sports with, you know, players having heart attacks. I don't know exactly why that is. Or collapsing."
In temperatures that touched 42.4 degrees, Canada's Frank Dancevic fainted during his match and Chinese player Peng Shuai cramped up and vomited.
And Daniel Gimeno-Traver had to rescue a ball boy who collapsed during his match with Milos Raonic. High temperatures in excess of 40 degrees were forecast to continue this week.
"It's definitely something that you maybe have to look at a little bit," Murray said, when asked whether or not he thought the conditions were safe enough to play in.
"As much as it's easy to say the conditions are safe - a few people said there's doctors and stuff saying it's fine - it only takes one bad thing to happen.
"And it looks terrible for the whole sport when people are collapsing, ball kids are collapsing, people in the stands are collapsing. That's obviously not great.
"And I know when I went out to hit before the match, the conditions like at 2.30pm, 3pm were very, very, very tough conditions. Anyone's going to struggle in that heat."
He said players were already pushing themselves to the limit and the heat adds to the physical burden.
"You don't want to see anything bad happen to anyone," he said.
Canada's Dancevic lashed out at the "inhumane" playing conditions after he felt dizzy and then blacked out and needed treatment during his first-round defeat to Benoit Paire.
"I think it's inhumane, I don't think it's fair to anybody, to the players, to the fans, to the sport, when you see players pulling out of matches, passing out," he said.
"I've played five-set matches all my life and being out for a set-and-a-half and passing out with heatstroke, it's not normal.
"Having players with so many problems and complaining that it's too hot to play. Until somebody dies, they'll just keep going on with it and putting matches on in this heat.
"I personally don't think it's fair and I know a lot of players don't think it's fair."
Officials said because humidity remained low, they chose not to invoke emergency rules that allow them to halt play and close the roofs on the centre and second court.
"Of course there were a few players who experienced heat-related illness or discomfort, but none required significant medical intervention after they had completed their match," said chief medical officer Tim Wood.
The Australian Open, held at the height of the Melbourne summer, is notorious for its heat. State officials on Tuesday imposed a blanket fire ban and warned of extreme temperatures in some areas of Victoria.
To cope with the hot conditions, players draped themselves in ice-cold towels, wore ice packs and guzzled water on the changeovers as temperatures, already at 35 degrees before play even started, rose steadily until early evening.
"It felt pretty hot, like you're dancing in a frying pan or something like that," said defending women's champion Victoria Azarenka.
"I don't think anybody wants to go outdoors right now."