About 200 metres of overhead power cables were damaged Engineers are working through the night to try to return East Coast Main Line services to normal after overhead power cable damage caused rail chaos.
The problem meant trains were unable to run between Peterborough and Grantham, affecting thousands of passengers on the route between London and Aberdeen.
Network Rail said it expected to be back to a full timetable by about 0900 BST, although some services may be hit.
Train operator East Coast said 70 of 102 scheduled services were disrupted.
A spokesman for infrastructure company Network Rail said it would be “all hands on deck” overnight to fix the damage in time for Sunday morning’s timetable.
Government-owned rail company East Coast said tickets for travel on Saturday would be valid on Sunday.
Shuttle services were running between London King’s Cross and Peterborough in Cambridgeshire, and north of Grantham in Lincolnshire.
Passengers travelling from London were also advised to use alternative services from St Pancras or Euston, where crowds of people tried to board trains.
Passenger Lucy Bannister, travelling from Brighton to Bradford, had been due to catch a service from King’s Cross.
She was directed to St Pancras, where she said the station was “chaos”, and later managed to get a Virgin train at Euston.
About 200 metres of overhead equipment was damaged between Stamford and Grantham, affecting all four lines on the route.
An East Coast spokesman said: “The cause is still being investigated. We will be looking into exactly what happened.”
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