Armed police officers were deployed to Green Park Tube station this afternoon, after receiving reports that there was a man with a knife in the area.
British Transport Police carried out a thorough search of the station and surrounding location, but said there was "no trace of anyone carrying any form of knife of other weapon".
"The sighting of a weapon has not been verified, though we believe the report was made in good faith."
Trains were prevented from stopping at the station while the alert was underway, but are now stopping as normal.
One eyewitness said 25 police officers had "stormed" Green Park as part of the searches.
Omg something is happening at green park station they won't let us on the train and loads of police have come down!— Lydia (@LydiaEmillen) December 8, 2015
Armed police checking an underground train at Green Park— Simon Walsh (@SimonWalsh91) December 8, 2015
BTP added: "Tensions are understandably high at the moment and we continue to ask all rail passengers and staff to report any concerns or suspicious behaviour to us."
It comes just days after a man attacked another at Leytonstone in east London.
The suspect, named as Muhyadin Mire, was remanded in custody and yesterday appeared in court charged with attempted murder. The 56-year-old victim was left with "serious" stab wounds in what the prosecution is now arguing was a terrorist attack.
Following this attack, BTP said it would be "deploying still more officers" to "identify and deter terrorism".
"They involve both uniformed and plain-clothed officers, supported by other resources, such as armed officers, police dogs, a network of CCTV cameras, and the thousands of rail staff we work alongside," assistant chief constable Mark Newton said on Sunday.
“We ask the public to remain calm and carry on using public transport as normal."