Qualifying rounds for the Australian Open were delayed Wednesday as toxic smoke from widespread bushfires continued to choke Melbourne, throwing the Grand Slam's schedule into chaos.
The decision to suspend the action followed heavy criticism when players were affected by hazardous conditions after play was allowed to go ahead on Tuesday.
One qualifier retired with breathing difficulties and Canadian Eugenie Bouchard needed medical attention, although all other matches were completed.
Play will not begin before 1:00 pm (0200 GMT), 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.
"EPA advises people in smoke-affected areas to take care, stay indoors away from smoke where possible and limit exposure."
Some relief may be on the way. The Bureau of Meteorology said thunderstorms and wind changes were expected for Victoria later Wednesday, which could clear the air.
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.
Qualifying for the first Grand Slam of the year, due to start next week, got underway an hour 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.
She sympathised with organisers but said that there "just has to be some line in the sand".
"Like the heat rule, there should be an air quality rule," she told reporters. "Maybe this tournament will help get that into gear".
Other 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.
The Kooyong Classic exhibition tournament, also taking place in Melbourne, looked set to start on time at 1:00 pm with organisers tweeting that "the excitement continues today".
Croatia's Marin Cilic is due on court first against South Korea's Kwon Soon-woo.
On Tuesday, Maria Sharapova's match against Germany's Laura Siegemund at Kooyong ended early partly due to the smoke, although later games went ahead without incident.
Despite the conditions, organisers have said it was unlikely the Grand Slam would be delayed.
Even if there is a repeat of this week's smoke, they have pointed to Melbourne Park having three roofed stadiums and eight other indoor courts that would allow play to go ahead.
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.
A fundraising exhibition match on Wednesday evening to raise money for bushfire relief efforts, featuring Roger Federer, Serena Williams, Rafael Nadal and others, will not be affected as it will he held with the roof shut on Rod Laver Arena.
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