Police in Edmonton are warning parents in Alberta and across the country that several students at local high schools have been caught using e-cigarettes to get high.

Electronic cigarettes, which are growing in popularity across Canada, are battery-powered devices that heat liquid flavour cartridges, nicknamed “juice,” to produce a vapour that resembles smoke.

Police say students are replacing the typical “juice” with marijuana oil. Because the oil in e-cigarettes does not emit the typical marijuana odour, it’s hard for school staff and police officers to realize what the students are “vaping.”

Police have already caught five students using marijuana oil in e-cigarettes over the last two weeks, but they suspect many more students are doing it undetected.

“It’s prevalent, it’s everywhere. Kids are jumping on this pretty quickly,” Sgt. Kelly Rosnau of the Edmonton Police Service told reporters Thursday at a news conference.

Rosnau, of the Edmonton Police School Resource Officer (SRO) Unit, says many school staffers have seen it happening, but remained unaware of what exactly was happening under their noses.

“In talking with teachers, with SROs, they're now realizing that in the past they saw these devices and really were unaware of what they were or what they were being used for,” he said.

Rosnau says police are worried by the trend because marijuana oil is much more potent than the marijuana contained in joints.

“The primary concern is the health of the youth,” he said. “Marijuana oil may contain a content of THC as high as 90 per cent compared to the 10 to 20 per cent THC levels typically found in marijuana or joints.”

Both Edmonton public and Catholic schools have since banned all e- cigarettes from school property, and have sent out letters to parents alerting them about the trend.

But police warn it's not just Edmonton parents and schools who need to be on the lookout.

“They're not just in the city of Edmonton. They're in the rural areas, the suburbs,” says Staff Sgt. Pierre Blais of Alberta Law Enforcement Response Teams (ALERT).

Rosnau says monitoring what people are vaping in e-cigarettes is difficult for officers.

“We have to have reasonable, probable grounds if we’re going to enforce the laws,” he said.

“But we can do so much more because our officers are working in a positive light with these kids. They know who they are. There's rapport building. And that goes a long way to dealing with these situations.”

With a report from CTV Edmonton’s Amanda Anderson