MELBOURNE, Australia (AP) — With extreme temperatures hitting Melbourne Park on Tuesday, the Australian Open was again set to institute the tournament's Extreme Heat Protocol, which works on a scale based on environmental conditions including the actual temperature.

Australian Open organisers invoked their extreme heat policy as temperatures soared at Melbourne Park on Tuesday, prompting the suspension of play on outer courts and the closure of roofs on the main showcourts.

Tournament organisers postpone the wheelchair events and will start play early on outside courts in anticipation of extreme heat in Melbourne on Tuesday.

It's one of the hottest days in Melbourne since 2009 and the Australian Open's heat policy has come into effect.

The Australian Open suffered more disruption Tuesday when it hit its maximum "heat stress" rating with forecasts of 45C, meaning the day's remaining quarter-finals will take place under a closed roof until the weather relents.