Toxic air pollution from unprecedented bushfires forced a halt to practice sessions Tuesday ahead of the Australian Open in Melbourne, the year's first tennis Grand Slam tournament.
Alexander Zverev and David Goffin were due on the Melbourne Park courts first, followed by world number one Rafael Nadal.
Stefanos Tsitsipas, Coco Gauff and Karolina Pliskova also had sessions booked in the lead up to the tournament starting on Monday.
"Practice was temporarily suspended this morning due to poor air quality," organisers said in a statement, although qualifying matches were set to go ahead.
"Conditions onsite are improving and are being constantly monitored."