Flights have been disrupted after the fuelling system was damaged by a lightning strike at Stansted Airport.
There were cancellations and delays after a thunderstorm and lightning strikes overnight.
The fuelling system was repaired on Sunday morning, but passengers were warned to check before travelling.
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The airport said in a statement: "Due to an earlier lightning strike, the aircraft fuelling system was unavailable 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.
"We apologise for the inconvenience and advise all passengers to check with their airlines for their latest flight updates."
Ryanair could not say how many of its flights had been affected, and said customers can get a full refund or free transfer.
"A number of flights have regrettably been cancelled at Stansted Airport this morning due to an earlier airport fuelling system failure, caused by a lightning strike," a 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.
"We apologise to all customers affected by these disruptions, which are entirely beyond our control."