Due to a widespread fault impacting the automatic border control gates that scan passports upon arrival, passengers flying into Britain experienced significant delays after landing at airports on Saturday.

Images shared on social media showed lengthy lines at London’s Heathrow and Gatwick airports with hundreds of people, and angry travelers lamented having to wait for hours in line.

“We are aware of a nationwide border system issue affecting arrivals into the UK,” said a spokesperson for the British government’s interior ministry, which has oversight of border control.

“We are working to resolve the issue as soon as possible and are liaising with port operators and airlines to minimise disruption for travellers,” they told Reuters.

Heathrow, Britain’s busiest airport, said it had deployed extra staff to manage the queues and was working with Border Force to help resolve the problem.

While many foreign visitors to the UK need to see a border control officer upon landing, others, including British, EU and U.S. citizens, can use the automated gates known as e-gates to scan their passports and enter the country.

The disruption, which comes during a busy period for travel in Britain with a spring bank holiday on Monday and a half-term break for schools next week, means all passengers have to be processed at manual checkpoints.

“What’s going on @HeathrowAirport? Just landed to scenes of utter chaos. 2 hour queues just to get to the real queue,” one passenger posted on Twitter.

British airlines and airports have faced other disruption over the past year including from separate strikes involving airport staff and Border Force workers as well as cancelled flights caused by staff shortages last summer.