A bomb disposal team has been sent to Gatwick Airport after suspicions were raised about a van.
Part of the West Sussex airport's North Terminal car park was cordoned off after concern was reported about a car that entered the ground level.
Sussex Police said that officers who responded to the alert at 2.40pm on Wednesday afternoon were unable to locate the driver of the Renault van or view all of its interior.
Inspector Gary Medland, from Gatwick Police, said: "We are aware that this is likely to cause significant disruption to people arriving or departing North Terminal by car, especially at this time of day.
"However, it is important that we establish whether this vehicle poses any threat and the cordon has been put in place for the safety of everyone visiting and working at the airport.
"There is no suggestion that there are any other threats to the airport and both police and security staff are actively checking all areas.
"However, as always, everyone should be aware of security and if they see anything suspicious they should report it to police officers or airport staff or dial 999 immediately."
Gatwick Airport said there have been no flight cancellations from the North Terminal and they hoped to open the terminal car park area soon.