Hopes of containing Australia's months-long bushfire crisis rose Tuesday with heavy rain forecast, but toxic smoke in Melbourne disrupted warm-up events for the year's first tennis Grand Slam.

Cool weather over recent days had already given some respite for exhausted firefighters spread out across vast swathes of the country, allowing some of the biggest blazes to be brought under control.

AFP / John SAEKI

Optimism was further boosted on Tuesday with heavy rain forecast for some of the hotspots in the most populated eastern states of New South Wales and Victoria.

"It's some pretty good news," New South Wales Rural Fire Service commissioner Shane Fitzsimmons said.

"We've been talking about it for months now, that January might see the first fall of decent rain, and that looks like what's coming along over the next few days."

Heavy rain is forecast for parts of bushfire-hit Australia, but it is too late for some places
Heavy rain is forecast for parts of bushfire-hit Australia, but it is too late for some places AFP / PETER PARKS

The rain was set to begin across eastern Australia on Wednesday and last through the weekend, according to government meteorologist Sarah Scully.

"Hopefully some of this heavy rainfall will fall over some of the fire sites and help control or even extinguish some of those fires," Scully said.

However dozens of fires remained out of control and, with many weeks of hot weather still expected throughout the rest of Australia's summer, there was no suggestion the crisis would completely end soon.

Smoke from bushfires - combined here with fog - has created huge problems for people across fire-hit areas
Smoke from bushfires - combined here with fog - has created huge problems for people across fire-hit areas AFP / SAEED KHAN

Toxic smoke from the blazes also blew overnight into the Victorian capital of Melbourne, which is due to stage the Australian Open tennis tournament beginning next week.

The governmen's response to the bushfire crisis and its continued support of the fossil fuel industry has come in for criticism
The governmen's response to the bushfire crisis and its continued support of the fossil fuel industry has come in for criticism AFP / Mohammad Farooq

Pollution in Melbourne, which is normally ranked as among the world's most liveable cities, was rated "hazardous", and health authorities warned people to stay indoors.

World number one Rafael Nadal and other stars abandoned outdoor practice sessions and hit indoors.

But Australian Open qualifying rounds went ahead after a two-hour delay in the morning, causing anger and confusion for some players who said matches should have been cancelled for the day.

Soaring pollution halts Australian Open practice and delays qualifying on Tuesday as smoke from raging bushfires hit the build-up to the season's opening Grand Slam.
Soaring pollution halts Australian Open practice and delays qualifying on Tuesday as smoke from raging bushfires hit the build-up to the season's opening Grand Slam. AFPTV / Tania LEE

Slovenian Dalila Jakupovic, ranked 201 in the world, had to retire from her match after suffering a coughing fit, and she later blamed the smoke.

"I was really scared that I would collapse... it's not healthy for us," she told reporters.

"I was surprised, I thought we would not be playing today but we don't have much choice."

Smoke haze from the bushfires raised air pollution to 'hazardous' levels days before the Australian Open tennis tournament starts
Smoke haze from the bushfires raised air pollution to 'hazardous' levels days before the Australian Open tennis tournament starts AFP / William WEST

Mandy Minella, the world number 140 from Luxembourg, also voiced her opposition on Twitter.

"Shocked to see that qualifying matches have started @Australian Open, What about the health of all the people that have to work out there, especially the ballkids?" she tweeted.

An exhibition match involving former world number one Maria Sharapova was also called off because of the smoke.

The hazy conditions were not expected to last all week in Melbourne, with a change in wind direction and the forecast wet weather set to clear the city's air by Wednesday night.

However Tuesday's drama raised concerns about whether the two-week Australian Open, which is often played in extreme heat, could be interrupted by another smoke surge.

Novak Djokovic, president of the ATP players council, had already said last week that the tournament may need to be delayed if the pollution levels were too high.

Organisers have said there is little chance of it being delayed.

The bushfires have killed at least 27 people, destroyed more than 2,000 homes and burnt 10 million hectares (100,000 square kilometres) of land -- an area larger than South Korea or Portugal.

Australia endures bushfires every summer.

However climate change and a prolonged drought have contributed to the current crisis, with the blazes starting much earlier than normal and lasting for far longer.

Australia experienced its driest and hottest year on record in 2019, with its highest average maximum temperature of 41.9 degrees Celsius (107.4 degrees Fahrenheit) recorded in mid-December.

Environmental groups estimate one billion animals have been killed, many of them unique to Australia.

The country's environment minister Sussan Ley has warned that in some areas, koalas may have to be reclassified as endangered.