UPDATE: Terminal reopened

NEW YORK, Jan 16 (Reuters) - A security breach prompted the evacuation of an American Airlines terminal at John F. Kennedy International Airport in New York on Saturday, the airline said.

Terminal 8 was cleared for several hours and thousands of passengers had to be rescreened after the breach, which happened shortly after 3 p.m. (2000 GMT), American spokesman Charley Wilson said.

The Transportation Safety Administration and the Port Authority of New York and New Jersey, which has jurisdiction over the three major metropolitan area airports, ordered the evacuation. Passengers who had boarded also had to get off their planes.

Local television reported that someone opened a door restricted to airport and airline employees, triggering an alarm. The incident was captured on security video but the person had not been found, NY1 news said.

Wilson said no inbound flights had been diverted, and that outbound flights at the terminal were expected to be delayed by two hours or more. There were no American Airlines flight cancellations.

"All clear at the terminal ... and we're getting things back to normal," Wilson said.

A security breach at Newark International Airport on Jan. 3 prompted a shutdown that delayed thousands of passengers at the end of the holiday weekend.

Authorities a week ago arrested the man suspected of setting off the scare, and charged him with defiant trespass. Security video showed the man slipping into a secure area at the airport to give a woman companion a goodbye kiss.