Emergency services were called to the car park of the Nations Church in King Edward St at 10.47am.
Detective Senior Sergeant Rob Hanna said the man died later in the morning.
His death was not suspicious and would be referred to the coroner, he said.
A man working across the road said by the time he saw smoke, the crowd had almost extinguished the fire with water.
He went to his vehicle nearby to get his fire extinguisher and helped them, he said.
Det Snr Sgt Hanna said police were working to notify the man’s next of kin. He was believed to have been in his late 50s.
"We are extremely grateful to the members of the public who went to the man’s assistance and who managed to put the fire out."
Those people were "incredibly courageous", he said.
"Police will ensure support is offered to those who helped or witnessed the incident."
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