Australia and England braved what is believed to be the hottest conditions seen for a Test match in this country on Sunday as the hosts close in on another heavy victory.

In weather better suited for a day at the beach or a day inside air-conditioned surrounds, a crowd of 33,285 sweltered as temperatures soared well into the 40s.

Players were given an additional break each session though the sight of players rushing out drinks became common on one of Sydney's hottest days on record.

A heat stress tracker, which records environmental factors to produce a "feels like" temperature, produced a reading of 57.6 degrees out in the middle of the ground.

England spent the hottest part of the day in the field as they struggled to make headway into Australia's batting. Several players wore cold wet cloths around their necks which were regularly replaced.

Wicketkeeper Jonny Bairstow ditched his baggy blue cap in favour or the wide brimmed floppy, presumably for extra sun protection.

Shaun Marsh, meanwhile, has a superstition where he does not wear sunscreen while batting, which may have him feeling better at the crease though not necessarily after his career.

"They're not used to that extreme heat," he said of the English.

The Bureau of Meteorology doesn't have a station at the SCG but nearby readings recorded temperatures of 43.4 to 43.7 degrees, above the 43.1 during the Adelaide Test of 1908.

It was not just the players doing it tough. Photographers and cameramen were supplied hydration powder by Cricket Australia's strength and conditioning man Aaron Kellett.

Fans not fortunate enough to be sitting in the boxes or in the stands had to find alternative methods to handle the heat. At one point, scores of spectators in the Noble and Bradman Stand gravitated towards seats that fell under the shadow of the curved roof.

Century-maker Mitchell Marsh grew up playing in the heat of Perth but had never experienced anything like Sunday.

Although there is a view the fielding team does it tougher in the heat, batsmen wear extra layers of padding and protective gear.

"This morning was one of the hottest conditions I've batted in in Australia," Marsh said.

"Even in warm-up it was boiling hot. It was a challenge to get through that today. Luckily these days with 12th man available to run out we get plenty of drinks and a few glove changes here and there to get us through."

Shaun Marsh said: "It was extremely hot out there. I had to try and concentrate, it was all we could do. We've played in hot conditions before, we've just got to get through it."

For England, it was another long day at the office. The visitors are staring down the barrel of another big loss. They claimed only five wickets in two days and if not for Steve Smith's declaration would have struggled to dismiss Australia.

"Not the hottest day but it would be one of the toughest certainly," said England's assistant coach Paul Farbrace.

Conditions are expected to be cooler on Monday but the mercury is still expected to rise to 33 degrees.