LONDON — Large parts of Britain were hit by a power cut, affecting trains, knocking out traffic lights and disrupting an airport during rush hour on Friday evening.

London, the southeast and northwest of England and Scotland were affected, leaving hundreds of thousands of people temporarily without electricity.

National Grid, which owns the electricity transmission system in England and Wales, said there had been “issues” with two power generators and the problems have now been resolved.

Members of the public posted images on social media, which showed the underground tube network in the darkness and people having to use their mobile phones as torches.