The London Overground has been suspended between Highbury & Islington and Clapham Junction, New Cross, Crystal Palace and West Croydon.
Dalston Junction, Haggerston and Hoxton are also affected this afternoon (Thursday, October 28).
Transport for London has said this is because of a fire alert at New Cross Gate.
Other parts of the Overground network have not been affected.
There are also minor delays on the Metropolitan line.
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