UPD:

The Metropolitan Police says in a statement:”To date police have not located any trace of any suspects, evidence of shots fired or casualties.

“Officers continue to work with colleagues from British Transport Police in the area of Oxford Circus.

“Updates will be provided as soon as we have them.

“If you are in building stay in a building, if you are on the street in Oxford Street leave the area.

“Officers are continuing to search the area.”

Armed police have descended on Oxford Circus Tube station after gunshots were fired in the station and on Oxford Street. Shocking footage shows huge groups of people running away from the station in central London following the incident on Friday afternoon.
Other photos of the area show a large number of police vehicles at the scene. In a statement, the Met Police said officers have responded ‘as if the incident is terrorist related’. The force said: ‘Police called at 16:38 to a number of reports of shots fired on Oxford Street and underground at Oxford Circus tube station.
Police have responded as if the incident is terrorist related. ‘Armed and unarmed officers are on scene and dealing along with colleagues from BTP.
A spokesman for British Transport Police said: ‘Officers are responding to reports of an incident at Oxford Circus station. Officers are on scene, more information when we get it. Follow @BTP for updates. ‘We continue to respond to an incident at Oxford Circus. The station is currently closed, please avoid the area at this time. Officers are on scene.’ TfL said workers were dealing with a ‘customer incident’. A spokesman for TfL said: ‘Oxford Circus is heavily restricted on all approaches to a Police incident. Avoid are if possible.’\

source: metro.co.uk