All plane departures have been halted in the United States under a "national groundstop" order, the Federal Aviation Administration (FAA) said today.
It is the first national groundstop in US history.
"We have a national groundstop order, which means no aircraft are taking off right now," said FAA spokeswoman Ms Laura Brown. The order was indefinite, she said.
"It is a measure we took because we thought it was prudent," Ms Brown said.
Trans-Atlantic flights heading into the United States were being diverted to Canada, said another FAA spokesman, Mr William Shumann.
Within the United States, aircraft in flight may continue to their destinations, the FAA said. "The planes in the air will land at the discretion of the pilot and the airline involved," said Ms Brown.
The FAA was unable to identify any of the aircraft involved in the US attacks, nor whether any threats had been received in advance, the FAA spokeswoman said.
No planes had received permission to fly over New York airspace, Ms Brown said. The airspace over New York was classified as "B", which means all planes must receive special permission to fly, she said.
- The Federal Aviation Administration said it was diverting transatlantic flights headed for the United States to Canada after earlier grounding all flights in response to three planes hitting major US landmarks in New York and Washington. AFP