Victoria Station was evacuated on Saturday afternoon due to a "person on the tracks".
There was major travel disruption as a result of the incident on the Victoria line platform at about 4pm.
The Victoria line was suspended between Brixton and Warren Street, with severe delays still being reported on the rest of the line.
Confused rail passengers earlier reported being evacuated from the busy hub station amid an "emergency".
A photograph posted on social media showed an air ambulance landing next to Buckingham Palace, a short distance from the station.
Meanwhile other pictures show a number of emergency services vehicles at the scene of the incident.
District and Circle Line trains were also initially suspended but have since resumed stopping at the station.
It is not known whether anyone was hurt in the incident.
A Transport for London spokesman confirmed that the station was closed due to a person on the tracks.
He added that tickets will be accepted on the local buses, Southeastern, South West Trains, Great Northern and the London Overground.
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