A man has been stabbed in a Costa coffee shop on Bowes Road, near Arnos Grove Tube station, North London, he is said to be in a critical condition.
Police and paramedics were called to the scene of the incident shortly after 11:30GMT.
One man was arrested at the scene and taken into custody, Metropolitan police confirmed.
The London Ambulance Service (LAS) said the victim was believed to be in his early 20s, was treated at the scene of the incident, they added that the victim was taken to a major trauma centre “as a priority” by road.
The scene has been cordoned off while police investigations take place. Transport for London said several bus routes have been diverted as a result.