A signal failure at Finchley Road was causing severe delays on the Metropolitan Line this morning, while a power outage was preventing Victoria Line trains from stopping at Blackhorse Road station.
Transport for London has been reporting delays on the Metropolitan Line since around 5am this morning, but by 7am was advising commuters to use the Jubilee Line instead.
The delays originally affected stations between Harrow on the Hill to Aldgate but as rush hour kicked in, TfL warned that the whole line was affected.
Tickets are being accepted on local buses and on Chiltern Railways, TfL said.
There are also delays on the Piccadilly Line between Cockfosters and Acton Town because of an earlier faulty train at Manor House.
Meanwhile a local power failure at Blackhorse Road meant that no Victoria Line services were stopping at the station.
This problem also appears to have started at around 5am this morning.
Walthamstow Central has also been closed because of a faulty escalator.