AN alleged armed robber who tumbled out of the back of a moving police van at a busy Perth intersection may have kicked the door, which was possibly not secured properly, the force says.

Dash cam footage of the handcuffed man falling onto the road as the van turned into Newcastle Street in Northbridge on Sunday afternoon was viewed thousands of times after it was posted to the Facebook page Dash Cam Owners Australia on Monday morning.

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Acting assistant commissioner Greg Knott said the 31-year-old man was on his way to the Perth Watch House after being arrested by Cockburn police in Munster and charged over an armed robbery at a West Perth liquor store last month.

Officers heard a thud then saw via live footage of the rear pod that he had got out.

One of the officers gave chase and caught the man within about one minute, roughly 150 metres away.

The incident is being probed by the police conduct investigation unit.

“As to how the door became opened, we’re not entirely sure,” acting assistant commissioner for the metropolitan region Greg Knott told reporters.

“We suspect that he may have somehow forced the door – we don’t believe he’s fallen out – however I’m prepared to leave that open to the investigators.”

It was possible the door, which has two latches, had not been properly secured, he said.

The man, who suffered no injuries, may have kicked it.

Police Minister Michelle Roberts said the incident was very disturbing.

“It’s obviously very important that prisoners are properly secured and kept safe,” she said.

“I don’t know whether there’s any failure in terms of locking the van procedure or whether there’s a mechanical fault.”

Mr Knott said it was a concerning incident but not embarrassing for police.

“These incidents thankfully don’t happen often,” he said.

“If there are things that need to be changed, we’ll do that.”

The man was also charged with failing to comply with reporting obligations, breach of bail and escaping from lawful custody.