Qualifying for the Australian Open Grand Slam was delayed Wednesday as toxic smoke from widespread bushfires continued to shroud Melbourne, organisers said.
The decision to push back the time players take the court followed a qualifier retiring with breathing difficulties on Tuesday and Canadian Eugenie Bouchard needing medical attention.
Play will not begin before 1:00 pm (0200 GMT), an hour later than scheduled, with practice sessions also suspended.
"Conditions at Melbourne Park are being constantly monitored," Tennis Australia said.
Further decisions will be made using onsite data in consultation with the tournament's medical team, the Bureau of Meteorology and scientists from the Victorian Environmental Protection Agency, it said.
The EPA listed air quality in Melbourne, habitually ranked as one of the world's most liveable cities, as "very poor" at 9:00 am but not at the "hazardous" levels registered on Tuesday.
Very poor means the air is likely smoky or dusty and that people might suffer coughing or shortness of breath.
The deteriorating conditions followed months of deadly bushfires that have engulfed huge swathes of the Australian countryside, leaving at least 27 people dead and more than 2,000 homes destroyed.
In a potential respite, the Victoria Bureau of Meteorology said thunderstorms were expected for the state later Wednesday, some of them severe with potential flash flooding.
Qualifying for the first Grand Slam of the year, due to start next week, also got under way late on Tuesday and Slovenian Dalila Jakupovic did not cope well.
She ended her match against Switzerland's Stefanie Voegele early after a coughing fit, saying: "I was really scared that I would collapse."
Former Australian Open semi-finalist Bouchard also had problems and needed a medical time-out after complaining of a sore chest.
Some players hit out for qualifying being allowed to go ahead, including world number five Elina Svitolina.
"Why do we need to wait for something bad to happen to do an action," she tweeted.
Despite the conditions, organisers have said it was unlikely the Grand Slam would be delayed, pointing to Melbourne Park having three roofed stadiums and eight other indoor courts.
Any smoke hazards will be treated in a similar way to extreme heat and rain, with umpires able to stop play if it is considered too dangerous to continue, they added.