The Australian Open has altered its schedule for the second time in four days because of extreme heat, with temperatures expected to reach 42 °C in Melbourne on Tuesday.

The start of the wheelchair events, featuring British defending champions Alfie Hewett, Gordon Reid and Andy Lapthorne, has been postponed until Wednesday, while play on the outside courts, where the junior matches are taking place, has been moved forward to 09:00 local time (22:00 GMT).

The four singles quarter-finals - which include world number ones Carlos Alcaraz and Aryna Sabalenka - and various doubles matches will take place on Rod Laver Arena and Margaret Court Arena, both of which have retractable roofs and air-conditioning systems which allow play to continue in cooler conditions.

Tournament organisers have not stated whether the roofs will be closed at the beginning of the day's play.

The Australian Bureau of Meteorology has issued a severe heat warning across the state of Victoria.

Matches were suspended on Saturday as temperatures climbed towards 40C and the heat scale hit its maximum of five, with play halted on the outside courts for five hours and action on the show courts continuing indoors.

The scale measures four factors - radiant heat (or the strength of the sun), air temperature in the shade, relative humidity, and wind speed.

'Some players in our category can't sweat'

Although all players are affected by the temperature extremes, Lapthorne has highlighted the additional physical challenges facing wheelchair competitors.

Speaking on BBC Radio 5 Sports Extra, the 35-year-old defending quad wheelchair men's doubles champion said: "There are players within our category that can't sweat if they've got a spinal cord injury.

"They don't have the ability to cool down, so it can be quite dangerous if they're in really extreme heat.

"I've had [cramp] in my forearms before because we're pushing a wheelchair as well as hitting the ball and once that gets hold you, it can be very difficult to stop."

While the tournament organisers have been proactive in responding to the weather, not only altering schedules but also providing numerous facilities to help fans cool down, not all players will get the benefit of playing under a roof.

"Do you know who suffers the most? The junior players. They are trying to play two junior matches at 09:00, before coming back at 18:30 and hoping it will cool down," BBC Sport's tennis correspondent Russell Fuller told the Australian Open Daily podcast.

"Those on at 09:00, it's still going to be boiling. It is tough for the juniors under those conditions. Some of them are 15, 16 years of age."

John Cain Arena - the third show court with a roof at Melbourne Park - is not scheduled to be used on Tuesday.

Sinner 'got lucky' with heat rule on Saturday

Men's second seed Jannik Sinner was among those impacted by the temperature on Saturday and admitted he "got lucky with the heat rule" during his four-set victory over world number 85 Eliot Spizzirri in the third round.

The Italian defending champion, who had lost the opening set, was a break down in the third and struggling with cramp when the scale hit its maximum, forcing the umpire to call play to a halt.

Sinner left the court during the eight-minute delay while the roof was closed on Rod Laver Arena and broke back immediately when play resumed before going on to win 4-6 6-3 6-4 6-4.

Under the roof, the temperature dropped to about 26 °C during the fourth set.

British junior Hollie Smart was also in action on Saturday and was forced to retire from her first-round match against Japan's Azuna Ichioka in the third set after struggling with cramp, leaving the court in tears.

In the men's and women's singles, it is the opposite side of the draw which will be affected by Tuesday's weather.

Why does Melbourne experience huge temperature swings?

By Elizabeth Rizzini, Lead weather presenter

If you look at Tuesday, you can see that the wind is coming from the north. That's because the very warm, dry interior of Australia is really heating up, with temperatures in the 40 °C in Alice Springs.

When you get that northerly wind, all of the heat is dragged down to Melbourne.

But when the wind switches to a southerly, we have colder air coming through from the Antarctic, and from Tasmania - and that's why we get these huge temperature swings in Melbourne in particular.

For that reason, we're all interested in Melbourne in the weather centre - but I imagine for the players and coaches it's a huge problem trying to predict what the weather's going to do - not from day to day, because the forecast sorts that out, but even just in terms of what to wear.