"Officers are on scene, more information when we get it", British Transport Police wrote.
The police have not located any casualties at this time.
"Officers are responding to reports of an incident at Oxford Circus station".
Police advised the public to avoid the Oxford Street area Friday.
One Twitter user said: "London's #OxfordCircus being evacuated and armed police on the scene".
"Police were called at 4:38 pm (1638 GMT).to a number of reports of shots fired on Oxford Street and underground at Oxford Circus tube station", London's Metropolitan Police said in a statement.
He added: "The police service acted extremely quickly and efficiently to secure and lockdown the area, demonstrating how incredibly well prepared they are to respond".
The station is closed while officers investigate the incident. Local residents said heavy police presence could be seen.
Witnesses on social media reported people running into nearby shops and pubs for shelter.
London's Metropolitan Police said there was no evidence of shots fired or casualties at the Oxford Circus tube station.
There was panic among rush-hour commuters and Black Friday shoppers in central London on Friday, with hundreds of people fleeing the scene.