A man has been taken to hospital in a critical condition after being stabbed in a Costa coffee shop.
Police and paramedics were called to the shop on Bowes Road, near Arnos Grove Tube station, North London, shortly after 11:30 GMT.
One man has been arrested at the scene and taken into custody, the Met has said.
The London Ambulance Service (LAS) said the victim, thought to be in his early 20s, was treated at the scene.
He was then taken to a major trauma centre "as a priority" by road, an LAS spokeswoman added.
The scene has been cordoned off by police. Transport for London said several bus routes have been diverted as a result.