The Victoria line on the London Underground has reopened after a power cut brought it to a standstill.
The line was suspended at about 07:00 BST, while passengers were also evacuated from Oxford Circus station due to power supply problems.
The Piccadilly line was suspended between Cockfosters and Hyde Park Corner because of the same issue, but has since resumed services.
Transport for London (TfL) warned there were still severe delays on the line.
The transport body apologised to customers affected by the disruption, explaining the issues had been "caused by a temporary loss of power at a number of locations across the network".
A spokesperson added: "Engineers are working as quickly as possible to restore a normal service."
Commuters have been advised to check their routes before they travel.
The disruption comes as mourners wanting to pay their respects to the Queen were warned to plan train journeys to London in advance.
The Rail Delivery Group said stations in the capital would be "extremely busy".
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