Australian Open organisers have imposed a three-hour delay to the start of qualifying matches on Wednesday because of the “very poor” air quality from ongoing bushfires in the country.
It is the second successive day the start of play has been delayed because of the conditions in Melbourne.
On Tuesday, Slovenia’s Dalila Jakupovic had to be helped off court after retiring from her match.
Air quality in the city did improve overnight but is still “unhealthy”.
Play will now begin at 13:00 local time (02:00 GMT).
In a statement, Tennis Australia said: “Practice has been suspended until 11am due to air quality concerns, and play won’t start before 1pm.
“Conditions at Melbourne Park are being constantly monitored and further decisions will be made using the on-site data and in close consultation with our medical team, the Bureau of Meteorology and scientists from EPA Victoria.
“The on-site data and measurements early this morning were similar to yesterday, when practice and play were suspended and delayed. Conditions yesterday were forecast to improve throughout the day, which is what occurred.”
According to the Environment Protection Authority in Victoria, the forecast is for improving conditions on Wednesday with a chance of a storm.
At least 28 people have died and an estimated 10 million hectares (100,000 sq km) of land in Australia has burned since 1 July.
The Rally for Relief exhibition match – featuring Roger Federer, Rafael Nadal and Serena Williams, with all money raised being donated to the bushfire relief fund – is scheduled to take place at Rod Laver Arena on Wednesday night.