Passengers have been stranded on trains for up to eight hours after a section of the overhead line came down on the West Coast Mainline.
The cable broke on the route between Lancaster and Preston early this morning blocking both lines in both directions, Network Rail said.
Transpennine and Northern trains have also been affected.
Three virgin trains were caught up in the disruption, with rescue trains needing to be sent to collect stranded passengers.
Passengers tweeted their frustration at being kept in the dark about what was going on.
Passengers have also been tweeting that there were no working toilets on the trains.
In a statement, Virgin Trains said: "We’re very sorry for the experience of customers affected by today’s disruption.
"We’re working closely with our partners to get customers from the affected trains to the nearest station so they can continue their journeys."
A Network Rail spokesperson said: "We’re sorry to passengers affected by the problems between Preston and Lancaster.
"This section of the West Coast mainline will be closed for the rest of the day while we fix a quarter of a mile of damaged overhead power lines.
Investigations are underway to find out exactly how the cables were brought down but our immediate focus is to fix the cables in time for the start of service tomorrow.
"We’ve been working closely with train operators to recover stranded trains today.
"Passengers are being advised by some operators not to travel this evening and tickets will be valid tomorrow. For latest travel information please check www.nationailrail.co.uk."
Network Rail's North West Director has also released an apology on Twitter.
Transpennine Express have tweeted that tickets will be available to use on other services tonight and tomorrow.