Players fainted and vomited and a ball boy collapsed as the Australian Open boiled in one of the hottest days in its history Tuesday, prompting angry complaints and keeping fans away in droves.

Temperatures of 42.2 Celsius, enough to melt plastic bottles on the rubberised courts, made for a punishing day for the players with some incensed their matches went ahead.

Canada's Frank 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.

"Having players with so many problems and complaining to the tournament that it's too hot to play... until somebody dies, they're just keep going on with it and putting matches on in this heat."

Chinese player Peng Shuai cramped and vomited during her loss to Japan's Kurumi Nara, and also received a violation for time-wasting at a moment when she said she was unable to walk.

"I had no energy, I couldn't run, I couldn't serve," she said, blaming the heat for her defeat. "So it's impossible to play tennis like this."

Officials said because humidity remained low, they chose not to invoke emergency rules which 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.

But Britain's Andy Murray warned organisers were taking a risk by allowing play to go ahead.

"Whether it's safe or not, I don't know. You've just got to be very careful these days," he said. "There's been some issues in other sports with, you know, players having heart attacks."

The Australian Open, held at the height of the Melbourne summer, is notorious for its heat. State officials imposed a blanket fire ban and warned of extreme temperatures in some areas on Tuesday.

The day's peak of 42.2 Celsius was shy of Melbourne's January record of 45.6 Celsius, which came during the notorious Black Friday bush fires of 1936.

Temperatures above 40 Celsius are expected for most of the week, in similar conditions to the 2009 Black Saturday bushfire disaster which killed 173 and injured hundreds more.

To cope, players draped themselves in ice towels and guzzled water on the changeovers as temperatures, already at 35 Celsius before play even started, rose steadily until the 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."

Daniel Gimeno-Traver helped a ball boy to his chair after he collapsed during the Spaniard's four-set loss to Milos Raonic. A spokeswoman said the boy later recovered with no ill effects.

And former women's world number one Caroline Wozniacki said that when she put her water bottle down on court, the bottom started melting.

"Geez, it feels hot out there," said Wozniacki. "It feels like I was sweating in a sauna or something."

Empty seats were prevalent as many fans stayed away, perhaps knowing how bad conditions have been in the past.

In 2009, the hottest edition on record with an average daily temperature of 34.7 Celsius, reigning champion Novak Djokovic pulled out of his quarter-final with Andy Roddick, citing heat exhaustion.

And in 2007, women's star Maria Sharapova slammed the conditions after playing a gruelling three-setter against France's Camille Pin.

Officials have sought to play down any health risks, pointing out that no player has ever died from dehydration on a tennis court.