Passengers travelling in rush hour from London have been hit by long delays.
Some affected reported being stranded on stationary trains for at least two hours.
Those on the West Coast Main Line are suffering severe disruption because of a signalling fault at London’s Euston station.
Network Rail apologised for the incident and said its engineers are “working to fix the problem as soon as possible”.
The West Coast Main Line runs between Euston and Glasgow with branches to major cities such as Birmingham, Liverpool, Manchester and Edinburgh.
Avanti West Coast issued an alert to passengers which stated: “Trains to and from London Euston may be cancelled or delayed due to a fault with the signalling system affecting multiple platforms at the station.”
Services operated by London Overground and London Northwestern Railway are also affected.
A Network Rail spokesperson said: “We’re so sorry for the disruption at Euston, and we’re doing everything we can to fix it.
“Our signalling system is designed to put signals to red if it detects a problem, a kind of safety ‘fail-safe’, and has done so on some of the tracks approaching the station this afternoon.
“We’re working with operators to run trains on the lines and platforms that are working as normal, but there are delays and cancellations as a result.
“We advise passengers to check with their operator before they travel to or from Euston this afternoon while we work to find and fix the problem.”
One affected passenger, Paul Carroll, posted on X, formerly known as Twitter, that he has been “stuck on a train for two hours not moving”.
Another passenger reported being “stuck on a train at Stockport for two hours”.
The disruption comes after Euston was closed for long-distance services between Good Friday and Easter Monday for engineering work, which included renewing the track between the station and Milton Keynes.