Dozens of bus passengers heading to the airport had to rush off the vehicle Thursday when it suddenly caught fire.

The bus had been driving on the Gardiner Expressway when the blaze began in the back of the vehicle. The driver pulled over near Spadina Avenue at about 8 a.m.

The fire was quickly extinguished by emergency workers, but not before the smell of burning metal filled the air, blowing in lakeshore residents' open windows.

None of the passengers were injured, although they were forced to get off the bus and stand on the side of the road until another bus arrived. 

Investigators don't know what caused the fire.