Passengers who flew to Britain today faced big delays after they landdue to an issue that arose at the country’s airports related to the operation of the automated screening gates, where passports are checked, after arrival in Britain.

Photos posted on social media showed long queues of hundreds of people at London’s Heathrow and Gatwick airports, with frustrated passengers complaining of several hours of delays waiting in queues.

“We have been made aware of an issue with the border security system across the country which is affecting arrivals into the UK,” said a spokesman for Britain’s Home Office, which oversees border controls.

“We are working to resolve the issue as soon as possible and are working with airport managers and airlines to minimize disruption to travelers,” officials told Reuters.