The Montreal Transit Corporation is reassuring riders about the safety of its service after someone posted a video on the internet showing a metro car travelling between seven stations with the doors wide open.

Transit officials have pulled the car from the fleet and are investigating.

The incident happened Monday shortly after 4 p.m. on the green line between the Langelier and Frontenac stations in the city's east end.

The 45-second video, posted on YouTube by a rider, shows passengers in their seats, capturing the scene on their cellular phone cameras as the metro car speeds through an underground tunnel.

At no point does an alarm sound, and the emergency brake is never engaged.

Transit corporation spokeswoman Marianne Rouette said maintenance crews inspected the car Monday evening and found the problem is isolated to the one particular door.

"The pieces of the door were sent to the lab. We want to know what caused the problem and ensure that it won't happen again," Rouette told CBC News.

Rouette said people travelling in the car should have pulled the emergency brake to alert the driver.

She reassured users about the safety of the city's 40-year-old metro cars, and said all the door mechanisms were replaced about three years ago.

"All of the rolling stock has our trust," she said. "What happened yesterday has nothing to do with the age of the rolling stock."

The Quebec government recently awarded a lucrative contract to Bombardier-Alstrom to build 500 new subway cars for Montreal over the next eight years.