Police are investigating two fires in North Adelaide early this morning, including one which spread through the Australian Medical Association's (AMA) state branch building.
Crews were first called to a brush fence set alight on Ward Street at about 2:15am.
Police then notified them of another fire lit in the car park under the AMA building on the other side of the same street.
Metropolitan Fire Service (MFS) fire cause investigator Marty Miller said the blaze was going in "numerous wheelie bins" when officers arrived.
"It's unfortunate these that wheelie bins were located adjacent to a main air conditioning unit for the building and the fire has travelled via an air conditioning duct to the main building," he said.
The blaze was brought under control but caused extensive damage to a dermatology clinic on the ground floor.
Mr Miller estimated the damage caused by the fire at between $1 million and $2 million, including to computers, medical equipment and the roof space.
Senior Constable Dave Muir from SA Police said it was believed the two fires were linked.
"Both fires have been deemed as suspicious and Eastern District detectives along with fire cause investigators are at the scene," he said.
"Anyone who saw any suspicious behaviour in the area around the time of the fires is asked to contact Crime Stoppers."
As well as the AMA, the building is also host to several specialists' clinics and the South Australian Salaried Medical Officers Association.
A unit behind the building was also damaged.
AMA state president Chris Moy said it would be "extremely disappointing" if it turned out the union was deliberately targeted by an arsonist but he suspected it was not the case.
"My sense is hopefully this is a random event," Dr Moy said.
"If this is a deliberate action, well that would be a very sad thing."
He said the dermatology clinic was "completely gutted" and some areas of the building could not be accessed while possible structural damage was being assessed.
"It's people first and building second, so it doesn't change our determination to keep on doing our job at the moment," he said.
"The AMA has had a really important role with what's been going on recently and we've just got to keep going."
