Some frightening moments for passengers on board a Grand River Transit bus in Cambridge.

The bus caught fire around 7 p.m. on Saturday near the Ainslie Street bus terminal.

“Suddenly we noticed a bit of a smell coming from the back,” said passenger Chris Wiedemann. “I looked at the back window of the bus and I see smoke just billowing out the back. I ran up and told the driver and the bus pulled over and everybody got off.”

Fire officials in Cambridge say the fire was caused by a malfunction in the engine compartment.

In a statement to CTV News, Eric Gillespie, Director of Transit Services said they are investigating what started tge fire.

“All GRT buses undergo regular maintenance inspections (every 2 months) and also comply with the Ministry of Transportation inspections every six months.”

According to Gillespie, a preliminary investigation points to a ruptured hydraulic line which caused hydraulic fluid to ignite.

Damage is estimated at $100,000, but if the bus can’t be repaired that amount could climb to $400,000.

With reporting from Mary Cranston