SYDNEY (REUTERS, AFP) - A water-bombing plane crashed in Australia's south-east on Thursday (Jan 23), as firefighters battled a new outbreak of bush fires whipped up by scorching temperatures and strong winds.

The Canadian-owned Hercules C-130 air tanker crashed while fighting bush fires in New South Wales' alpine region. All three victims were American residents, Australian authorities said, adding that they did not immediately know why the plane crashed.

"Tragically, there appears to be no survivors as a result of the crash down in the Snowy Monaro area," said Mr Shane Fitzsimmons, the Rural Fire Services Commissioner for New South Wales state.

"(The tanker) impacted heavily with the ground and initial reports are that there was a large fireball associated with the impact of the plane as it hit the ground. There is no indication at this stage of what's caused the accident."

Mr Fitzsimmons said the plane had been leased by Canadian aerial firefighting company Coulson Aviation, which has a second C-130 Hercules working in the Australian bush fires operation.

Coulson grounded its large air tanker fleet following the accident, pending a review to ensure there was no systemic issue like a fuel problem, Mr Fitzsimmons said.

The Canadian company has been operating under contract with the Australian National Aerial Firefighting Centre since 2000, according to the company.

Coulson said the plane was on a firebombing mission and was carrying a load of retardant. The company said it would send a team to the crash site to assist in the emergency operations.

"The accident is reported to be extensive and we are deeply saddened to confirm there were three fatalities," the company said in a brief e-mailed statement.

The crash takes the death toll from hundreds of wildfires in Australia to 32 since September. An estimated one billion animals have also perished, while the fires have incinerated 2,500 homes and a total area of bushland one-third the size of Germany. The authorities previously said the tanker was flying in the state's Snowy Monaro region, south of the capital Canberra.

Flight tracking website Flightradar24 showed the flight path for an air tanker used in water-bombing operations suddenly stopping in Peak View, south of Canberra.

According to its flight data, the aircraft departed the Richmond air force base in western Sydney around 12.15pm local time. It dropped off radar just after 2pm.

Peak View is close to a blaze burning out of control in the Wadbilliga National Park, the fire service said.

Bush fires also forced the closure of Canberra Airport, with all flights in and out of the country's capital suspended due to approaching flames. An update posted on Canberra Airport's website listed the carriers whose flights had been cancelled, including Singapore Airlines.

Passenger flights were halted around midday local time as two out-of-control blazes burning immediately to the south and west of the airport merged and the combined fire bore down on three nearby suburbs.

Temperatures soared to 40 deg C in Sydney, where a bush fire also broke out in a north-western suburb of Australia's biggest city.

Wind gusts had been forecast to reach 90kmh in some areas, but Rural Fire Service Commissioner Fitzsimmons said the winds were stronger than expected, especially in the fire-ravaged south-east of the state.

"One of the big challenges we've got with the increased intensity of these winds is that it is proving very difficult to fly any aircraft to provide any aerial support to the firefighting effort on the ground," he said.

"We are trying to get some of the large air tankers and some of the very large helicopters involved, but it's proving very difficult. It's too dangerous to fly these things."

Mr Fitzsimmons warned of a "long, difficult afternoon" ahead for firefighters and residents.

A LONG WAY TO GO'

Unprecedented bush fires fuelled by climate change have killed at least 29 people and devastated vast swathes of the country since September.

The blazes have been followed by extreme weather that has hampered cleanup operations in some areas, including intense storms that have battered parts of Australia with giant hail, floods and landslides.

Heavy rainfall has helped to contain and, in some cases, extinguish long-running blazes, but an expected return to searing heat and gusting winds on Thursday was flagged as a cause for concern as dozens of fires continued to burn.

Cooler weather was forecast to return on Friday, but the bush fire season still has weeks left to run.

"The fire season doesn't traditionally stop here in New South Wales until right up to the end of March," Mr Fitzsimmons said.

"So we've got a long way to go this season and whilst the rainfall has been certainly welcome and the conditions have eased, we're certainly not out of the fire season yet."

The months-long crisis has sparked renewed calls for Australia's conservative government to take immediate action on climate change, with street protests urging Prime Minister Scott Morrison to reduce the country's reliance on coal.

A major coal conference in Wollongong - situated in a coal-producing region south of Sydney that has been hit by massive blazes - was cancelled this week in response to what local climate activists said was a "planned mass protest".

And a January poll released this week found the environment has soared to the top of Australians' concerns, with 41 per cent of people polled by market research firm Ipsos ranking it as the most important national issue for the first time.

While Mr Morrison has now reluctantly acknowledged the link between the bush fire disaster and a warming planet, he has stopped short of announcing any sweeping new measures to cut emissions.

Instead, the prime minister signalled that his government would focus on climate adaptation and building resilience.