A prisoner escaped from a paddy wagon in Toowoomba while being escorted to a watch house in Brisbane this morning. He has since been arrested by police. Credit: Stuart McGavin

WA Police are investigating a viral video posted to Facebook today that shows a man falling out of the back of a paddy wagon into the middle of a busy intersection.

In the footage, which has been viewed nearly 170,000 times since being posted to the Dashcam Owners Australia page this morning, the police car makes a right turn after the light goes green.

As it does so, the apparently unlocked door swings open and a man in handcuffs falls out, rolling along the road.

The video is timestamped just after 1.50pm on November 10 and was taken at the intersection of Charles and Newcastle Streets in Perth.

"Police forgot to lock the back door of there paddy wagon. Unfortunately the dashcam didn't captcha him running away and... Posted by Dash Cam Owners Australia on Sunday, 10 November 2019

“Police forgot to lock the back door of there (sic) paddy wagon,” the Facebook page wrote, quoting the person who submitted the video.

“Unfortunately the dashcam didn’t captcha (sic) him running away and the police chasing him down the freeway.”

WA Police Assistant Commissioner Greg Knott said a report into the incident was being prepared by the Police Conduct Investigation Unit, which would speak to the officers involved and examine the pod door latch mechanism.

“As to how the door became open, we are not entirely sure, but it certainly was enough for him to escape from the vehicle and run from police,” Mr Knott told a media conference.

“Obviously police were going in one direction, he ran in the other. I believe he wasn’t running across traffic. As far as I know there was no danger to himself.”

The 31-year-old Northbridge man had been arrested in Munster at around 12.30pm in relation to an armed robbery of a liquor store in West Perth on October 27.

“The man was handcuffed and placed in the rear of a police van to be conveyed to the Perth Watch House,” Mr Knott said.

“As the vehicle proceeded through the intersection, officers were made aware that the man was no longer in the rear pod.”

The officers realised he had escaped when they “heard the thud and then checked the camera for the pod and realised he had exited the vehicle”.

“An officer exited the vehicle and pursued the man on foot, apprehending him a short time later — within a minute, we think about 150 metres,” Mr Knott said.

He said it was believed the man had somehow forced the door open, possibly by kicking it, rather than falling out.

“However I’m prepared to leave that open to the investigators to find out what has occurred in this case,” he said.

He explained that the police van door has two latches, one as it closes and another mechanism that comes across the door and closes it again “so it’s double secured”.

“There are procedures as to how that’s supposed to have been done and that will be part of the investigation,” he said.

Mr Knott said he had heard of this happening, “over a long history, in previous days and times, a long time ago, but yes — but different vehicles, different mechanisms, a whole different type of set-up than today with the pods”.

“It’s one of those things that does happen,” he said.

“I wouldn’t say embarrassing, but it’s certainly not a good thing to happen — and if there’s something we need to fix and something we need to change in relation to our procedures or there is some issue with the mechanism of the vehicle then we need to fix that.”

He added, “It is concerning when people escape from custody but you’ve got to consider, we transport significant numbers of prisoners and people every day across the metropolitan area and regional WA, so these incidents thankfully don’t happen often and when they do we investigate them.”

WA Police Minister Michelle Roberts earlier told PerthNow she had been advised of the incident but not yet had a full briefing.

“It is clearly very disturbing,” she said.

“I haven’t been fully briefed on it, clearly there will need to be an investigation. It is a very serious matter … senior police will investigate.”

The man appeared in Perth Magistrates Court this morning charged with armed robbery, failure to comply with reporting obligations, breach of bail — and escaping from lawful custody.

He is not believed to have suffered any injuries. “Certainly nothing that required medical attention,” Mr Knott said.

frank.chung@news.com.au