Services to and from Paddington railway station remain disrupted after hundreds of passengers were stranded on dark, cold trains for several hours.
Damage to overhead electric cables in the Ladbroke Grove area of west London affected Elizabeth line, Great Western Railway and Heathrow Express trains.
Some passengers reported being stuck for more than three hours while receiving little or no information.
Engineers managed to open two lines for electric trains serving Paddington.
Major disruption is expected until 15:00 GMT, with trains in and out of Paddington cancelled or delayed. GWR has advised customers to avoid travelling between London and Reading until further notice.
Elizabeth line trains are running with delays, while a reduced half-hourly service is running on the Heathrow Express.
A Network Rail spokesman said: "We are so sorry for the difficult journeys passengers endured on our railway last night and we will be investigating how and why it happened.
"The knock-on effects from last night mean operators will not be able to run a full service from Paddington today and passengers should check before they travel.
"Repairs are ongoing and we hope to have the railway fully open by the weekend."
'Really eerie'
The £19bn Elizabeth line - which opened in May 2022 - uses mainline rail infrastructure west of Paddington.
Paddington services have been repeatedly affected by rail system faults in recent weeks - incidents on the Great Western line include four damaged rails discovered in eight days last month.
TV personality Rachel Riley was among those affected. She posted on X: "Nearly 4 hours after we got on, we're getting off the Elizabeth line, woohoo!"
Singer James Blunt also claimed to have been caught up in the chaos.
Blunt wrote on X: "Been stuck somewhere outside Paddington for close to 4 hours now. Out of peanuts and wine".
