The Metropolitan Police were called at 4:38pm on Friday afternoon after there were reports of shots fired at the station.
It comes on one of the busiest nights for the station as Black Friday shoppers make their way home.
Several people were injured and nine were taken to hospital in the incident at Oxford Circus Tube station, London Ambulance Service said. "Avoid area if possible". "If you sought shelter in a building please now leave, and follow the direction of police officers on the ground if you need assistance", the force said on Twitter.
This includes the Royal Variety Performance at the nearby London Palladium going ahead as planned, although the arrival of the Duke and Duchess of Cambridge had been delayed.
An armed policeman runs down Oxford Street in central London on November 24, 2017, as police responded to an incident.
"Armed and unarmed officers are on scene and dealing along with colleagues from British Transport Police". The Metropolitan Police has confirmed its officers are also attending.More news: Fort Bend Owners of Anti-Trump Bumper Sticker Threaten Civil Rights Lawsuit
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Videos on social media showed people running along the streets.
"At this stage, we are examining the circumstances of the incident which resulted in the station being evacuated".
"I was next to the tube station and everyone started screaming and shouting and then a flood of people came up the stairs", local man Greg Owen told reporters. It was a very panicked scene.
"Police have responded as if the incident is terrorist related".
"This is a very high footfall area and safety and security are number one priorities for everyone working in the district".
The police said they found no evidence of any suspects or any gunfire and informed the public that it was safe to return to the area.