The runway at Gatwick has been closed to all flights because of a spillage, a spokesman for the airport said.
No flights have been able to land or take off at the West Sussex airport since around 10.30am.
An airport spokesman said a number of incoming flights have been forced to remain in the air and the "priority" will be to allow them to land as soon as safety checks have taken place on the runway.
The cause of the spillage has not been confirmed.