MELBOURNE, Jan 27 - 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.

The tournament's "Heat Stress Scale" reached the highest threshold of 5.0 early in the afternoon with the temperature breaking through the 40 Celsius (104F) mark by 2 p.m. -- the hottest day of the tournament so far.