Mounties in Langley are sounding the alarm over party bus celebrations after a 17-year-old girl was seriously injured during a ride this weekend.

RCMP stopped a vehicle operated by Vancouver Party Bus around 10:30 p.m. Friday after officers witnessed two girls tumble out of a side door while the bus was turning left at Highway 10 and Fraser Highway.

One of the girls appeared unconscious and unresponsive, officers reported.

The injured girl was rushed to hospital where she was listed in serious condition. Her condition was upgraded to stable within several hours and she was released later that night. The other teen was uninjured.

Witnesses told police a passenger on the bus, one of nearly 30 young people on board for a 17th birthday party, pushed the emergency exit open during the turn.

Investigators spoke to the group, all 16 and 17-year-olds said to be in "varied levels of sobriety," and released them after taking statements.

A "substantial" amount of alcohol was seized from the bus, RCMP Const. Holly Marks said. With grad season right around the corner, Marks says parents need to be aware of where their children are, especially if there is potential for alcohol to be involved.

"There are lots parents out there that would think this is a safe way to go out for a party – because they're all contained in the bus – but it's just not," she told

"If liquor is being consumed you've got young people drinking alcohol, dancing and a vehicle stopping and starting in traffic in the Lower Mainland it's a recipe for disaster."

Mounties are still considering charges.

A manager with the Vancouver Party Bus company told safety is their number one priority, especially with an underage group. The manager, who asked only be identified as Shelley, said all the alcohol seized by police was alcohol its staff had taken from passengers – and that no alcohol is allowed on any of their vehicles.

Shelley said the bus driver had a hard time with the group throughout the evening, and was forced to yell at them several times not to open the emergency door.

"These buses have been on the road for multiple years and this has never ever happened before. This happened earlier in the trip -- the driver told them not to do this again," she said.

Shelley said the person who opened the door, "a friend of a friend of a friend," was not well known by the other passengers.

"This created a hazardous circumstance and two innocent girls were hurt," she said.

The youngsters were accompanied by a 35-year-old chaperone. The company said at least one person over the age of 18 must be present on any bus trip where young people are on board.

The bus was impounded for investigation after the incident. An inspector from the Commercial Vehicle Safety and Enforcement Branch completed a safety and mechanical inspection on the vehicle but the results have yet to be made public.

Vancouver Party Bus says the vehicle is "perfectly safe."

The company said it would consider installing a siren that would alert drivers if someone touched the emergency exit to prevent further incidents. It is also considering having patrons sign contracts promising not to bring alcohol on board.

"We want to create a fun evening where kids can have a party atmosphere. We have no alcohol -- we give them great music -- we drop them off at home. This is supposed to be safe," Shelley said.

"We're just shocked about this."

The bus company shuttles up to 1,500 passengers on Friday and Saturday nights.