British meteorologists said thousands of lightning strikes hit the U.K. during a powerful overnight thunderstorm, and a London-area airport reported flight disruptions Sunday after an aircraft refueling system was damaged.

London Stansted Airport said that a lightning strike disabled the fueling system “for a period this morning. Engineers have been on site and have now restored the system, however flights may still be subject to diversion, delay or cancellation.”

More than 200 flights were delayed at Stansted. Another 31 departures and 18 arrivals were cancelled, according to FlightStats, which provides data on commercial aviation.

London-area airports were busier than usual, since Britain is in the middle of a long holiday weekend, and many schoolchildren also have a half-term break this coming week.

Budget airline Ryanair, which has a big presence at Stansted, couldn’t say how many of its flights had been affected at the airport, but was offering full refunds to some.

The Ireland-based airline apologized to those affected, but said the disruptions were beyond the company’s control.

“A number of flights have regrettably been cancelled at Stansted Airport this morning due to an earlier airport fueling system failure, caused by a lightning strike,” a Ryanair spokesman said. “All affected customers are being contacted and advised of their options of a full refund, a free transfer on to the next available flight or a free transfer on to an alternative routing.”

Meteorologist Charlie Powell said information suggested there were “somewhere between 15,000 and 20,000 strikes across the U.K. during the overnight period.”

Morning!
Did you sleep well?
Possibly not if you were in the south of the UK. Around 50,000 flashes of lightning recorded across central and southern England, Wales and around the English Channel overnight 🌩😴
Matt pic.twitter.com/azWsNkmfeV

— BBC Weather (@bbcweather) May 27, 2018

(AP)