For now, there is no evidence of injuries to the police, and the agencies report a mildly injured woman in the crowd while escaping from the metro station.
The British Transport Police has said it believes an altercation took place on a tube platform at Oxford Circus station, where Regent Street and Oxford Street meet.
Armed police run along Oxford Street, London, Britain November 24, 2017.
The Oxford Circus station is at the heart of London's shopping hub, Regent Street, and is only minutes away from Piccadilly Circus. The shop is locked and police have whole area on lock down'.
Passengers then "self-evacuated" onto the street, causing a "significant level of panic which resulted in numerous calls from members of the public reporting gunfire", the statement said. Police found no evidence any weapons had been fired.
Oxford Circus station reopened soon afterward.
Anyone with any information should contact British transport police on 0800 40 50 40 or text 61016 citing reference 405 of 24/11.
At the height of the panic, The Daily Mail online posted a story - seemingly based on a 10-day-old tweet - saying witnesses had reported "seeing a truck surrounded by police on a pavement covered with blood".
"We were in the Kingdom of candies and then saw a massive crowd of people running and screaming".
'Officers are continuing to search the area'.
Eyewitnesses reported being caught in "stampedes" and said there was "pandemonium" as police treated the incident as if it was terrorist-related. "I think people were so unsure what had happened they were running in all directions".