A commuter bus caught fire Thursday on a Los Angeles-area freeway, and 27 people were treated for smoke inhalation, a fire official said. No one was seriously injured but the bus was gutted.

The northbound Commuter Express bus was at Calabasas, about 12 miles northwest of Los Angeles, when the fire broke out in the engine compartment in the rear, authorities said. The cause was not immediately known.

"The driver noticed smoke and then some flames coming out of the rear," Los Angeles County fire Inspector Steve Zermeno said. The driver pulled over and the 37 passengers got out.

One woman who suffered smoke inhalation was taken to a hospital for observation, and 26 other people were treated at the scene for smoke inhalation, Zermeno said.

Except for the woman who was hospitalized, the passengers resumed their trip on another bus.

The Los Angeles Department of Transportation, which runs Commuter Express buses, did not immediately return a call seeking further detail.