LONDON (AP) — Travellers arriving in the UK faced hours-long delays Saturday after a technical problem shut electronic border gates at airports across the country, forcing everyone to have their passports checked manually on what was expected to be one of the busiest travel weekends of the year.

The Home Office, the government agency responsible for immigration and borders, said it was working to correct a “nationwide border system issue,” though it provided no details about what caused the problem.

Airport operators asked for patience and apologised for the delays as frustrated travellers took to social media to post photos of long lines at airports including Manchester in the north of England and London Heathrow, Europe’s busiest airport. Travel is expected to be especially busy over the next few days as a three-day weekend coincides with the start of a week-long holiday for most schools in Britain.

“We are aware of a nationwide border system issue affecting arrivals into the UK,” the Home Office said in a statement. “We are working to resolve the issue as soon as possible and are liaising with port operators and airlines to minimize disruption for travelers.”

The problems, which began Friday night, come as U. airports, airlines and ferry operators try to rebuild goodwill with the public after a series of glitches caused travel chaos last summer when foreign travel surged following the coronavirus pandemic.

Electronic passport gates are automated self-service barriers designed to speed up processing of travel documents. Using facial recognition technology, the system verifies a traveller’s identity against the data stored in the chip in their passport.

There are now 270 such gates at 15 air and rail ports in the UK, according to the Home Office. They are open to anyone over the age of 12 who holds a passport from the U.K., any European Union member country, Australia, Canada, Iceland, Japan, Liechtenstein, New Zealand, Norway, Singapore, South Korea, Switzerland and the United States.

Heathrow and other airports promised to do what they could to ease congestion.

“We are aware of a nationwide issue impacting the eGates, which are operated by Border Force,” Heathrow said in a statement. “This issue is impacting a number of ports of entry and is not Heathrow specific. Our teams are working closely with Border Force to help resolve the problem as quickly as possible and we have additional colleagues on hand to manage queues and provide passenger welfare.″