A teenager has died after he was stabbed outside a block of flats in west London.

The victim, who was 17, was found with knife wounds by police next to a block of flats on Union Lane in Isleworth at 10.30pm on Friday evening as officers responded to reports of a fight in the area.

Despite performing first aid on the boy he was pronounced dead shortly after paramedics arrived.

No arrests have yet been made but the Metropolitan Police said a murder inquiry has already begun.

A couple who called the police have described their shock at finding the bloodied teenager on the floor.

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They heard shouting outside their flat and looked out to see two people, one wearing a mask, assaulting the boy who was lying on the floor.

"It was one guy who was massive with, like, a mask on his face and another small guy.

"They were kicking him, but it was dark so it was hard to see exactly what was happening," the husband, a 33-year-old engineer who did not want to be named, said.

His wife, 35, added: ""The boy was bleeding from the mouth. The blood was everywhere.

"He was still alive, there was someone else there trying to help by checking his pulse. He was responding but he couldn't speak."

Another neighbour, Halima Abubaker, said she had seen two men "running for their lives" around the time of the attack and then saw at least seven police cars and two vans.

"I've lived here two years and nothing like this has happened. I feel really sick."

A Met spokesman said: “A post-mortem examination and formal identification will be arranged in due course. Officers have begun the process of informing next of kin.

“An urgent investigation is underway, led by detectives from the Homicide and Major Crime Command supported by colleagues from the West Area Command Unit.”

London Mayor Sadiq Khan described the incident as an "appalling, senseless act of violence", adding: "The family and friends of this young man are in my thoughts at this awful time."

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Last year murders in London hit a ten-year high of 154 and new government figures released last week showed knife and weapon offences were at their highest level for nine years across England and Wales.