Commuters were left stuck "for an hour" on the Elizabeth Line on Tuesday evening as several major west London routes were brought to a standstill by a power supply problem.
Great Western Railway and Elizabeth Line services between London Paddington and Reading were forced to close, alongside Elizabeth Line services to London Heathrow.
Some commuters complained they were trapped on the Elizabeth Line for an hour as severe delays also hit the Elizabeth line between Paddington and Abbey Wood.
National Rail said a failure of electricity supply between London Paddington and Maidenhead meant some lines were blocked.
One person posted on X: "Been stuck on the Elizabeth line for an hour I think all passengers deserve compensation to be honest what is this.”
A second traveller posted: "We stuck on Elizabeth Line train for over 1 hour now! I will be missing my flight tonight if I cannot get there in next hour!!! We stuck on train please emergency release the doors!!!"
A commuter posted: "First day back at work and the Elizabeth Line starts the year as it means to go on. Delays and suspended."
Tickets are being accepted on buses, London Underground, the DLR, Thameslink, GWR and local bus services. There are minor delays on the rest of the line.
A statement from Great Western Rail said: "Network Rail are currently investigating an issue with the overhead wires between London Paddington and Slough, where a loss of power earlier today had caused trains to come to stand.
"Power has now returned, meaning that trains are able to run again on some lines."
The disruption comes after around 4,000 travellers were forced to wait about four hours to be rescued when seven trains – four Elizabeth line, two Heathrow Express and one Great Western Railways intercity service – were brought to a halt near Ladbroke Grove last month.
Passengers on the packed Elizabeth line trains, including families heading into central London for Christmas shows, and travellers who had landed at Heathrow were eventually led along the tracks to safety.
Network Rail told the Standard this was a different issue from what affected overhead lines in the disruption before Christmas.
A Network Rail spokesperson said: "There was a power outage just outside London Paddington which caused delays and cancellations for some Elizabeth line services.
"We have now re-energised the overhead line equipment and trains are on the move. We are sorry for any disruption caused to passengers and advise people to check before they travel as delays may continue while we clear the backlog."
