A man is fighting for life after being attacked outside a Tube station in north west London.
The incident happened at around midnight on Saturday, the Metropolitan Police said.
Officers were alerted by medics after the man was brought into a central London hospital for treatment, where he remains in a critical condition.
Police are continuing to work to establish his identity and appealed for any witnesses to come forward.
Detective Sergeant Emma Thompson, from the North West Command Unit, said: “We know from CCTV that there were people in the area outside Burnt Oak Tube station at around midnight who saw what happened and I would urge anyone with information to come forward.
“A man is lying critically ill in hospital as a result of this act of violence and we need to find who is responsible.”
Anyone with information is asked to contact police on 101 or ‘X’ @MetCC and quote CAD1419/28Oct.
Witnesses can also provide information anonymously to the independent charity Crimestoppers on 0800 555 111.