More armed police are patrolling the front of the terminal at Stansted Airport and vehicles have been barred from the area.
Armed patrols at the Essex airport have been stepped up
The patrols at the Essex airport were stepped up after a burning car was driven into a terminal door at Glasgow.
The airport said passengers must be picked up and dropped off at car parks.
There may be significant delays in reaching the terminal using the airport shuttle buses so passengers are asked to allow extra time.
It said passengers could still reach the airport by public transport and this helped to avoid delays.
There is no disruption to services because of the extra security, but it may take longer for passengers to be checked in.
Police also said they would be making more use of stop and search under the Terrorism Act and there would be patrols by armed response vehicles around mainline train stations.