Passengers are being urged not to travel on London North Eastern Railway (LNER) services between Edinburgh and London after damage to overhead wires caused major disruption.
The incident happened at around 10:30am between Grantham and Peterborough on the East Coast Main Line, which runs between London, Yorkshire, the North East and Scotland.
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LNER issued an alert "advising customers not to travel today" as trains are being cancelled, delayed by up to two hours or diverted.
Services operated by East Midlands Trains, Grand Central and Hull Trains are also disrupted.
Network Rail, the government-owned company responsible for maintaining Britain's rail infrastructure, said it would investigate the cause of the damage.
In October last year a Class 802 Hitachi train was being tested ahead of its handover to Great Western Railway (GWR) when it brought down overhead wires in west London, crippling London Paddington services.
A similar train model - a Class 800 Azuma - was the first to reach the damaged wires during Wednesday's incident but was not believed to be the cause of the fault, according to a rail industry source.
Electric trains use pantographs mounted on their roofs to take electricity from overhead wires.
A Network Rail spokesman said: "We would like to apologise to anyone who is currently experiencing disruption on the East Coast Main Line.
"This is due to a fault with the overhead line equipment in the Peterborough area. Network Rail engineers are on site and are working to resolve the issue as quickly as possible, however we expect disruption to remain until the end of the day.
"Passengers are advised to check before travelling with their train operator or via National Rail Enquiries. We are working closely with train operators to keep passengers moving where possible and we would like to thank all those who are impacted for their patience."