Even though Gatwick South terminal has reopened, widespread cancellations have begun to be made. British Airways has cancelled at least 30 flights to and from the Sussex airport.

European and North African flights from Gatwick have been grounded to Tenerife, Marrakech, Malta, Faro, Porto, Malaga, Alicante, Seville, Jersey (two), Bordeaux, Verona, and Turin.

Long-haul flights to Trinidad and Islamabad are cancelled. All the related inbound flights are also grounded.

An estimated 5,000 passengers have been affected.

Thousands of passengers who have sought refuge in North Terminal at Gatwick – as the only place for some distance with warmth and catering – are now queuing for the shuttle to get back to South Terminal.

In addition, there is confusion over the status of Gatwick airport railway station. It is open and trains are stopping, but the message has gone out that it will not reopen until 4.15pm.

An update from the Gatwick Express have warned that delays are expected until 4.15pm, despite the lines reopening.

A statement read: Lines have reopened following the police dealing with an incident at Gatwick Airport earlier today. Trains may still be delayed by up to 20 minutes or revised.

“This is expected to continue until approximately 4.15pm.

“For the latest flight information and updates, please check directly with your airline operator.”

Nejadeen Braham, 35, who works as a nurse on the Isle of Man, was due to fly to her homeland of Jamaica to collect her children.

Speaking to reporters outside the south terminal, she said: “I couldn’t get in the airport. I saw everybody coming (out) from one direction.

“I was supposed to go inside, drop my bags and go through security. When I got here I saw everybody coming down.

“There were no proper updates. I’m very frustrated.”

A London Gatwick spokesperson said: “The earlier security alert has now been resolved and cleared by police. The South Terminal is reopening to staff and will be open to passengers shortly.

“Trains will also start calling at Gatwick Airport once the terminal is fully reopened. We would like to thank everyone for their patience and understanding while this situation was resolved. Safety and security is always our top priority.

“There are some delays and cancellations, passengers should contact their airline for any updates on flights.”

Passenger information website National Rail Enquiries said: “The police are dealing with an incident at Gatwick Airport. The station and airport are currently being evacuated.

“Services are able to run through the station and area but will not call at Gatwick Airport at this time.

“Please avoid travelling to the station whilst this incident is ongoing.

“This is expected to continue until approximately 2pm.”

Aviation analytics website Cirium said 316 flights are scheduled to depart from the airport on Friday, with a total of more than 60,600 seats.

A further 318 flights are scheduled to arrive, with more than 61,400 seats.

An airport hotel allowed some stranded passengers to go in to get warm and charge their phones.

British Airways is advising passengers to check information online before travelling to Gatwick Airport.

A spokesperson told The Independent: “Like other airlines, we are experiencing some disruption to our flight schedule at Gatwick due to a security incident at the airport’s South Terminal.

“We are in contact with affected customers and giving them updates as and when we can. We’re also providing them with options including flight rebookings and hotel accommodation where necessary.

“We ask customers to check ba.com for the latest flight information before coming to the airport.”