A woman has died and five others were injured in a knife attack in Russell Square, central London.
Police and ambulance crews were called at 22:33 BST on Wednesday to reports of a man in possession of a knife and injuring people.
Up to six injured people were found at the scene; one woman was pronounced dead a short time later.
The man was arrested at 22:39; a taser was discharged by one of the arresting officers.
Terrorism is one possible motive being explored, the Metropolitan Police say.