Disruption of rail services in and out of London Euston station is expected to continue into the rush-hour after a trackside fire.
Signalling equipment was damaged in the blaze, temporarily cutting Euston's power supply and leading to its evacuation, Network Rail said.
Engineers hope to restore services as soon as possible but delays are likely, after the fire in South Hampstead.
The whole of the West Coast mainline was affected, as far as Liverpool.
Customers on London Midland, Virgin and Southern trains were all disrupted, with services affected at Clapham Junction and Milton Keynes Central.
The fire, which broke out on Wednesday afternoon, also had an impact on a stretch of the London Overground line between Euston and Harrow & Wealdstone.Image caption
Network Rail said: "Train customers are impacted in London and the length of the West Coast main line, including Birmingham, Manchester and Liverpool."
It said emergency generators had been brought in to provide temporary power to signals and help get trains moving.
"Engineers are preparing to work through the night to install 100 metres of 11,000-volt power cables, with the aim of getting services back to normal [on Thursday] morning," it added.
Customers on Virgin trains were advised not to travel south of Birmingham. It said tickets would be accepted for travelling on Thursday or passengers could get a full refund.
Passengers were advised to use services provided by Chiltern Railways, East Midlands Trains and Great Western Railway or check with National Rail Enquiries before travelling.
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