LONDON — Heathrow Airport is warning passengers to check their flight status after problems with runway lighting caused disruption.

Europe's largest airport said Wednesday that the problem had been resolved by 6:05 a.m GMT (12:05 a.m. EST) and that both runways are now open and operational. But travelers should check, as delays are expected throughout the morning.

Some flights were delayed up to three hours, and the problem left some London-bound travelers stranded on U.S. tarmacs.

Heathrow said in a statement that its engineering teams are investigating.