London Euston station has been evacuated and train services suspended due to a trackside fire.
Network Rail said the fire, near South Hampstead, north London, damaged signalling equipment.
The power supply to Euston station was temporarily cut as a result of the incident, leading to the evacuation.
Engineers hope to restore services as soon as possible but it is warned full timetables are unlikely to resume until Thursday morning.
The fire affected customers on London Midland, Virgin and Southern trains.
It also took out a stretch of the London Overground line between Euston and Harrow & Wealdstone.
Network Rail said: "An electrical fire at South Hampstead has stopped trains running in or out of London Euston this evening.
"Train customers are impacted in London and the length of the West Coast main line, including Birmingham, Manchester and Liverpool."
It added: "Network Rail engineers are trying to get some trains moving this evening on the West Coast main line by using emergency generators to restore temporary power to signals - the traffic lights of the railway.
"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 tomorrow morning."
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.
The BBC's transport correspondent Richard Westcott said: "If you are going anywhere near Euston tonight, frankly, I just wouldn't bother. The Tube trains are affected as well so make sure you don't travel unless you absolutely have to."
Passengers are advised to use services provided by Chiltern Railways, East Midlands Trains and Great Western Railway or check with National Rail Enquiries before travelling.