Part of the London Underground was suspended during the evening rush hour after a report of a man armed with a knife.
Police were called to Bank station shortly after 5pm and a large part of the Central Line was suspended for around half an hour on Wednesday evening.
Trains are now running again but with severe delays, Transport for London said.
British Transport Police said officers searched both Bank station and nearby Liverpool Street station but found "no trace of the man".
Investigations continue and police remain at both stations.