Euston station has been evacuated and closed due to a power cut, caused by a fire next to the tracks at South Hampstead.
Virgin Trains, London Midland and London Overground services are affected. Frustrated commuters posted pictures of the crowds outside Euston.
A Network Rail spokesperson said: “Trains are being delayed into and out of London Euston due to a line side fire near South Hampstead which has damaged signalling equipment. Network Rail has engineers on site trying to restore services as soon as possible.”