An incident in which a van packed with gas bottles exploded outside the headquarters of the Australian Christian Lobby (ACL) was not politically, religiously or ideologically motivated, police say.

ACL managing director Lyle Shelton tweeted the incident on Wednesday night, saying a vehicle had caught on fire outside its office in Canberra just after 9:30pm.

Mr Shelton added that staff were safe, and photos he shared showed a burnt-out van in the car park near the building's entrance.

ACT police confirmed a 35-year-old Canberra man had ignited gas cylinders in the van and caused an explosion, which damaged the vehicle and building.

Australian Christian Lobby managing director Lyle Shelton tweeted a photo of the burnt-out van. ( Twitter: @LyleShelton )

The man was the only person injured in the incident and walked himself to Canberra Hospital — a distance of just under 4 kilometres —with serious burns.

He was later transferred to Concord Hospital in Sydney where he remains in intensive care in a stable condition.

In a statement, police said their brief questioning of the man revealed his actions "were not politically, religiously or ideologically motivated".

'Strong smell of petrol in the air' By ABC News Canberra reporter Jesse Dorsett The first thing that hit me when I arrived in the Canberra suburb of Deakin early this morning was the strong smell of petrol or some other kind of accelerant. The van had already been removed from the carpark in a delicate operation just after midnight, but the tyres had melted onto the concrete, which tells us how hot the explosion must have been. There are also other remnants of the van scattered around the ground including the Toyota badge, a melted number plate and an air conditioning vent. We have just been allowed upstairs to Lyle Shelton's office. It's lucky no one was at work at the time because the windows have been blown in, glass thrown around the room, the blind is shredded and roof is also damaged. It is going to take some time to clean up here and repair the building.

The man was not previously known to police.

Mr Shelton said he hoped police were correct and that the ACL was not specifically targeted.

"But I don't think it's possible to definitively know from a statement given by a man pulled out from a burning wreck under great distress," he said.

Initially Mr Shelton was describing the blaze as a "targeted attack" on "free speech in Australia".

"We have received a number of death threats and threats of violence over the course of this year that we have reported to police," he said.

"This is an attack on free speech in Australia, which I am deeply shocked about and never thought I would see in my lifetime."

Federal Justice Minister Michael Keenan said there were "no ongoing safety issues for the ACT community".

"There's no indications that it's a terrorist act," he said.

Windows on ground floor blown out in explosion

Sorry, this video has expired ACL HQ damaged in van explosion

Mr Shelton said the ground floor windows of the ACL's offices were blown out by the force of the explosion.

"Fortunately none of our staff or the tenants in the building were there," he said.

"The building was vacant, it was after hours, so none of our people were injured."

The van has been removed from the site but part of its tyres have melted onto the concrete.

The incident comes two days after a vehicle burst into flames after being rammed into a building only a few kilometres away in Fyshwick.