Investigators were scouring Chicago's O'Hare International Airport on Saturday after an engine caught fire on an American Airlines plane attempting to take off on Friday, as a source said a detached engine part had hit a nearby building, something the design should have prevented.

No serious injuries were reported in the incident, which crippled a Boeing 767 with 161 passengers and nine crew members aboard as it was departing for Miami and briefly closed all O'Hare's runways.

The failure was so intense that a disk from the engine hit a building roof, according to a person familiar with the matter.

Jet engines are designed to keep parts within the outer cover as escaped shrapnel can tear through the cabin or rupture fuel tanks in the wings. Such "uncontained" failures therefore are extremely rare and National Transportation Safety Board officials were looking for clues as to whether the fault lay with the engine, with maintenance or a freak event such as debris on the runway entering the engine.