Fire officials are investigating the cause of a smoky fire that started in an HVAC unit at Fairfield Ludlowe High School Thursday morning, forcing evacuation of the building.

The fire, which broke out about 10:15 a.m., apparently started -- and was largely confined -- in the band room. Fire crews on the scene reported it was knocked down within about one-half hour.

The fire started somewhere in an HVAC unit, and was pumping smoke into the room, according to a preliminary investigation.

Ludlowe Headmaster Greg Hatzis said there were no injuries, and the evacuation went smoothly in accordance with the school's emergency plan.

Superintendent of Schools David Title, who was also on the scene, credited the emergency plan for guiding the school administration's prompt response.

The students have been relocated to the gym of nearby Roger Ludlowe Middle School because of the cold temperatures.

Westport firefighters provided backup coverage in town.