Extreme heat forced play to be halted Tuesday on outside courts at the Australian Open, with the roofs closed on its three main stadiums – Rod Laver Arena, Margaret Court Arena and John Cain Arena.

With players sweltering in 36 Celsius (96.8 Fahrenheit) temperatures, the tournament’s five-part heat stress scale hit five.

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

The lowest level reading is one and the highest five, at which point play is suspended.

“This means play continues until the end of an even number of games or the completion of a tie-break,” organisers tweeted.

“No new matches will be called to court. Play on outdoor practice courts is also suspended.”