Transport for London said parts of its train network were affected during the outage.
London CNN  — 

Trains ground to a halt, homes went dark and cars wandered through intersections without functioning traffic lights as large swathes of London and southern England temporarily lost power Friday.

All power has now been restored, according to UK Power Networks and to Western Power Distribution, which serves power to the Midlands, the South West region and Wales.

UK Power Networks tweeted that the outages were “due to an issue on the national transmission network,” adding, “we believe all supplies have been restored.”

Earlier in the day, the country’s National Grid Electricity System Operator tweeted about “issues” with two power generators.

Urban transportation was severely impacted by the outages, if only briefly.

A major London Underground line came to stop because of the outage, Transport for London confirmed to CNN, though by 6 p.m. that service was restored.

“The Victoria line was affected, but it is back up and running now. There are severe delays, though,” a TfL spokesperson told CNN.

The agency had urged caution on the roads, as some traffic lights went dark because of the outage. Major airports were not affected.

Londoners shared pictures of the power surge on Twitter, which showed the Tube network in darkness.

The outage also temporarily affected several overground train services, with Thameslink tweeting that its trains had been brought to a standstill, and London North Eastern Railway said several of its trains had broken down.

“Power supply problems are currently causing disruption to a large number of train services. Information screens in some areas are also affected,” National Rail Enquiries said, according to Britain’s Press Association.

Earlier Friday, UK Power Networks warned it was “preparing for forecast of strong winds” across the South East and East of England, directing customers to its website for further guidance on how power might be affected.