A 21-year-old man has been stabbed to death inside a north London shopping centre.
Police were called to reports of a group of males fighting at Brent Cross Shopping Centre at about 6.45pm on Tuesday.
Officers attended and found the victim, who had been stabbed.
First aid was started by members of the public and police, while London Ambulance Service and London Air Ambulance were also called.
However, despite the best efforts of everyone involved, the man died at the scene.
Police said efforts were underway to inform his next of kin.
An 18-year-old man was arrested nearby on suspicion of murder.
A second man, also believed to be aged 18, has been arrested on suspicion of affray.
Video footage posted on social media showed police officers evacuating the shopping centre and an air ambulance landing in the car park outside.
Privacy screens also appeared to have been put up outside an M&S store, while police tape cordoned off an area of walkway outside a River Island and Foot Locker.
Chief Superintendent Sara Leach, who is in charge of policing in northwest London, said: “My thoughts are with the loved ones of the young man who has been killed in this incident.
“I would like to offer my thanks to the members of the public who came to his aid. They showed considerable courage.
“Two people have been arrested and an investigation is already underway. We will do all we can to identify and bring to justice those responsible.
“The public can expect to see a heightened police presence in the area through the rest of this evening and in the days to come.”
The shopping centre was open at the time of the incident and it is likely there were a number of witnesses.
Anyone with information should call 101, providing the reference CAD6136/04MAY.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111.
The incident is not being treated as terror-related.