A man wielding a machete has stabbed a man in a Tube station in London.
A video apparently of the incident and posted on Twitter shows a large pool of blood spattered across the ticket hall as the alleged knifeman is Tasered by a police officer.
Terrified passengers, some with children, can be seen running across the east London Tube station away from the scene.
A Scotland Yard spokesman said: "Police were called at 7.06pm on Saturday 5 December to reports of a stabbing at Leytonstone Underground station. The male suspect was reportedly threatening other people with a knife.
"Met officers attended the scene. A man was arrested at 7.14pm and taken to an east London police station where he remains in custody. A Taser was discharged by one of the Met officers.
"Officers from British Transport Police are now dealing with the incident at the scene. We are aware of one man having sustained serious stab injuries. We await details of any other injuries."