An engine on a United Airlines plane briefly caught fire Tuesday just before it was to take off from Fort Lauderdale-Hollywood International Airport, an airport spokesman said.

Flames were seen coming from one of the plane's two engines as it was taxiing to the runway for a flight to Washington, D.C., but none of the plane's 138 occupants was hurt during the incident, airport spokesman Steve Belleme said.

It was unclear what sparked the fire, which was put out by fire-rescue workers. The incident shut down the airport's main runway for about 20 minutes, Belleme said.