The 35-year-old was airlifted from Canberra Hospital early Thursday evening to Sydney's Concord Hospital, one of two adult specialist burns units in New South Wales.

Police said the man parked a van and ignited several gas cylinders inside it outside the headquarters of the ACL building in the Canberra suburb of Deakin on Wednesday night.

ACL managing director Lyle Shelton was quick to label the fire a deliberate attack against the organisation's conservative political stance, but police determined there was no political, religious or ideological motivation behind the explosion after interviewing the man.

Speaking to Fairfax Media on Thursday, Mr Shelton cast doubt on police claims.

"There's a whole bunch of things that just don't add up," he said.

After the explosion it's understood the injured man walked nearly four kilometres from Deakin to Canberra Hospital, where police spoke to him for a short time before he underwent treatment.

The man's condition was initially deemed critical before his transfer to Sydney.

Mr Shelton told ABC radio the clean up of the ACL will begin in the new year while the organisation reassessed its security.

According to NSW Health, patients cannot be transferred between hospitals until their condition is stable.

More to come.