The Glades shopping centre in Bromley was the scene of an altercation between two men armed with knives.
Armed police have been called to a shopping centre in south-east London after reports of a man carrying a machete.
A video posted online appeared to show people running out of the Glades in Bromley during the Boxing Day sales.
London Ambulance Service said that a woman was being treated by paramedics at The Glades in Bromley.
Witness Ceri Harlin told the Evening Standard that "a police van pulled up and officers went running inside. Security and three or four police officers have handcuffed a man and the police officer is carrying the huge knife".
Police described the incident as an "altercation between two people," adding that they received a call 3.45pm to "reports of an injured man at the Glades shopping centre".
Officers arrived at the scene and found a man, believed to be in his 20s, with a head injury. A spokesperson for Scotland yard stated that "officers believe he sustained the injury as a result of an altercation. The injured man has been arrested for affray and possession of an offensive weapon. He currently remains in custody at a south London police station".
Officers recovered two knives, and are still looking to trace on a man who was seen running away from the scene, possibly discarding a weapon.