ONE of the planes that crashed into the Trade Center was American Airlines Flight 11, hijacked after takeoff from Boston en route to Los Angeles, the airline said.

American Airlines issued a statement saying it had "lost" two aircraft - Flight 11, with 92 people aboard, and Flight 77 from Washington to Los Angeles, carrying 64 people.

In Pennsylvania, United Airlines Flight 93, a Boeing 757 en route from Newark, N.J., to San Francisco, crashed about 80 miles southeast of Pittsburgh.

The fate of those aboard was not immediately known and it was not clear if the crash was related to the disasters elsewhere. In a statement, the airline also said it was deeply concerned about another plane, Flight 175, a Boeing 767 bound from Boston to Los Angeles.

US aviation authorities are reporting several planes are unaccounted for.

They are said to be in addition to the ones which have already crashed.

There are still reports that one aircraft is heading towards Washington.

ITN reports Canada is shutting down all airports.

World travel has been thrown into chaos. Many US-bound flights had already left the UK when American officials decided to close all US airports.

Officials at other America-serving UK airports, including Heathrow and Gatwick, are trying to cope with the travel backlog.

These airports, too, would have had passengers already in the air and heading for America, with hundreds of others due to travel later today.