Passengers have been advised to leave plenty of time for their journey to the airport as roads immediately around the terminal have been closed.
A 41-year-old Frenchman was arrested on Saturday at Britain's second busiest airport Gatwick with a weapon that appeared to be a firearm, following the evacuation of a terminal, police said.
"Due to an incident - the North Terminal has been evacuated as a precautionary measure. Extra staff on-site looking after passenger welfare," the Airport said.
Sussex Police said the Frenchman was arrested after he "discarded an item" at the airport.
"Personal items and what appears to be a firearm were recovered and have been removed for forensic examination. However, the viability of the weapon has yet to be established," Sussex police said in a statement.
The airport, Britain's second busiest, falls in West Sussex county of England, nearly 50 kilometres south of Central London. A spokesperson said that Explosive Ordnance Disposal specialists were at the scene.
Detective Superintendent Nick May said: "At this time, we are investigating the circumstances of the incident and it is too early to say what the item may be. However, given the events in Paris on Friday evening, there is heightened awareness around any such incident and it is best that we treat the matter in all seriousness."
Gatwick Airport has advised passengers to contact airlines for information. British Airways and Easyjet said they were working with the airport and the authorities to assess the situation and any potential impact on flights.
Passengers have been advised to leave plenty of time for their journey to the airport as roads immediately around the terminal have been closed. A statement from Gatwick Airport said passengers due to arrive into the North Terminal would be arriving into the South Terminal. It added that landside passengers who were already at the North Terminal were being looked after in nearby hotels. The terminal has since been partially re-opened.
UK airports and ports are currently on high alert following the terror attacks that shook France last night. Hundreds of people were photographed standing outside the airport in the rain after being told to leave the airport at around 10am GMT.
Passengers at the West Sussex airport were reportedly told to stay away from glass windows and pictures from those at the scene showed large crowds waiting outside in the rain. The Telegraph quoted 23-year-old web designer Ozay Booth as saying: "We were in the airport and then all of a sudden police started running and shouting 'everyone get out, get out'.
"It was terrifying! Particularly after everything that happened yesterday. They've put us all under a bus shelter but no-one's telling us anything. There must be 500 of us here but we don't know what's going on, it's awful."
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