Multiple signal faults around Peterborough mean that many trains from London Kings Cross are being heavily disrupted.
Lines affected include all Hull Trains, Grand Central, LNER and Lumo services to and from Kings Cross.
Trains on these lines may be cancelled or delayed by up to an hour.
Although the lines have reopened after Network Rail fixed the issue, disruption is expected until 1pm.
Other trains affected are CrossCountry services between Stansted Airport and Birmingham New Street and East Midlands Railway services between Peterborough, Lincoln and Doncaster, and between Norwich, Sheffield and Liverpool Lime Street.
LNER are recommending customers to delay their travel “due to the severity of today’s disruption”.
Operators are allowing customers to use their tickets on later trains or different services at no extra cost.
