Investigations are underway into the crash of a C-130 Hercules air tanker that was fighting bushfires in Australia’s alpine region, a state fire official said on Friday, with the state in mourning for three men killed in the accident a day earlier.

The premier of the state of New South Wales (NSW) ordered flags to be flown at half-staff on Friday as a mark of respect for the three victims, whose names have yet to be released.

“We will forever be indebted to the enormous contribution and indeed the ultimate sacrifice that’s been paid as a result of these extraordinary individuals doing a remarkable job,” NSW Rural Fire Service Commissioner Shane Fitzsimmons said on Friday.

He was speaking at a farewell to 32 U.S. firefighters, part of a North American contingent who have helped tackle the bushfires that have raged across the country since September.

The plane crash on Thursday took the death toll for the devastating bushfire season to 32. The fires have also killed millions of animals and destroyed a land area about one-third the size of Germany. (Graphic: https://tmsnrt.rs/30O47Eq)

The C-130 Hercules air tanker that crashed had been leased from Canadian aerial firefighting company Coulson Aviation, which said it was sending a team to the site to help with emergency operations. They are due to arrive in Sydney on Saturday morning, Fitzsimmons said.

The company is also flying out the families of the three victims, experienced aerial firefighters who were in their 40s, he said. Australian Transport Safety Bureau investigators are due to arrive at the site in the Snowy Mountains region on Friday.

“We simply don’t know the circumstances pertaining to the accident at this stage. Appropriate, formal investigations and inquiries are underway,” Fitzsimmons said.

He earlier said field reports showed there had been a “pretty significant fireball associated with the plane crash”.

While fire conditions eased in southeastern Australia on Friday, Sydney was choking on a new smoke haze, blown in by a baking hot wind from the fires burning in the south of the state. The harbourside city was also covered in a layer of terracotta-coloured soil brought in from the west by huge dust storms.