There is no trains service between Euston and Harrow after a fire.
National Rail said trains would be cancelled until 4.15pm.
The small fire broke out on a section of track near South Hampstead station, leading to all services in and out of Euston station being cancelled.
The afternoon blaze caused damage to signalling equipment and led to a power cut,causing massive disruption to travellers during the evening rush hour.
Victoria and Northern line Tube services were also hit.