Vancouver police are investigating after yet another porta-potty was set on fire in the city's downtown core.

The blaze started shortly before 10 p.m. on Tuesday in a portable washroom in an alleyway off Robson Street, between Hornby and Burrard Streets.

Video showed flames rising from the scene before firefighters put it out. After the fire, there was little left of the porta-potty other than a pile of molten plastic.

The VPD's Major Crimes Unit has taken over the investigation.

Since Dec. 9, a total of 19 porta-potties have been destroyed in a series of 11 arsons police believe are all connected.

"We have investigators currently working the case and trying to solve it—find out who this person is," said Vancouver police spokesperson Sgt. Jason Robillard.

Porta-potties are full of plastics and chemicals that burn quick and hot. While arsonists might think of these fires as practical jokes, authorities are warning that they can be extremely dangerous.

"It won't be a joke when it burns down a building. It won't be a joke when it kills or injures someone and it certainly won't be a joke when that fire kills or injures a firefighter," Fire Capt. Jonathan Gormick told CTV News.

"If they're adjacent to something, if they're near a building, a structure or vegetation, it wouldn't take much for the fire to spread to that and get out control probably before we can get there."

On Jan. 4, that's exactly what happened when a porta-potty fire spread to the Vancouver Art and Leisure building in East Vancouver and caused extensive damage.

On Wednesday, Jan. 24, fire crews responded to another blaze that destroyed a porta-potty outside the Blue Horizon Hotel on Robson Street.

Authorities have not released the locations of the other fires.

Anyone with information about any of the porta-potty fires over the past two months is asked to contact investigators at 604-717-3321.

Police say anyone with a portable washroom on their property should move it away from buildings, lock it overnight and remove the toilet paper and hand sanitizer.

With files from CTV Vancouver's Shannon Paterson