A teenager has been stabbed to death in broad daylight in a shop as thousands of bargain hunters thronged one of Britain's busiest shopping streets.
The 18-year-old from south London was killed in the Foot Locker store on Oxford Street, London, as "hundreds of thousands" of people shopped nearby on the opening day of the post-Christmas sales, the Metropolitan Police said.
Police said it was too early to establish what the motive for the stabbing was.
Seven arrests have been made and a crime scene has been set up which runs from Duke Street to New Bond Street, near Bond Street underground station.
A forensics team erected a white tent in front of Foot Locker, overlooked by Christmas lights.
Confused Boxing Day bargain hunters and tourists were coming up to the police cordon to take pictures and ask officers what had happened.
Shoppers could be seen going in and out of shops near the crime scene, such as Debenhams and Zara, but a number of stores have been forced to close.
An employee at the nearby Disney Store said: "We are being quite badly affected, we are unlikely to open again today."
Boots was also closed, an employee confirmed, but the Body Shop remained open.
Police said they were called at around 1.45pm to reports of a stabbing.
London Air Ambulance and London Ambulance Service also attended but the man was pronounced dead at the scene.
A spokeswoman for the New West End Company, which represents traders on Oxford Street, Regent Street and Bond Street, declined to comment on the stabbing or the effect on retailers on one of the busiest shopping days of the year.
But earlier, the company reported £15 million sales in the first three hours of the Boxing Day sales despite a drivers' strike on the London Underground.
Jace Tyrrell of the New West End Company said: "As ever, the West End's Boxing Day sales have attracted shoppers in their hundreds of thousands."
Three years ago, Steven Bigby, from Hackney, was killed in broad daylight on Oxford Street.
The 22-year old was stabbed to death outside a McDonald's restaurant in May 2008 when a row erupted after a drink was thrown.
Anthony Costa, 19, of Walthamstow, east London, was jailed in December that year for the attack on Mr Bigby, who was on police bail at the time having been arrested over the rape of a 16-year-old who had caustic soda poured on her in Tottenham, north London.
Costa was given an indeterminate sentence for public protection and told he would serve at least five years by Judge Richard Hawkins at the Old Bailey after being found guilty of manslaughter.
In August this year, two teenagers were stabbed outside H&M on Oxford Street in front of hundreds of horrified afternoon shoppers.
The 18-year-old man and a 15-year-old boy survived the attack, which prompted road closures in the area.
A total of 10 people have been arrested in connection with the murder, police confirmed.
Senior investigating officer Detective Chief Inspector Mark Dunne, from the Metropolitan Police's Homicide Command, told journalists gathered at the scene that the murder had taken place at the "busiest place in the United Kingdom on the busiest shopping day".
He said it was still not clear whether the incident had happened inside or just outside the Foot Locker store.
He said: "A number of weapons have been recovered from that scene, whether I have got the murder weapon I don't know. There's an assortment of items but no guns.
"My officers and many other officers from the West End are looking to get as many witnesses as we possibly can and to get a full account of exactly why this happened."
Mr Dunne said it seemed that there had been a confrontation between two groups of youngsters and confirmed that "a number of people" had been arrested.
"We are in the process of speaking to them and speaking to some witnesses who have already come forward.
"This is probably the busiest place in the United Kingdom right now on the busiest shopping day so it's been difficult for us to piece together what has happened and clear this area to do the job we are paid to do and work out a sequence of events here.
"The flipside of that is we have probably more witnesses than we would normally have and I'm very much looking forward to them coming and speaking to us."
Police confirmed that another stabbing took place today close to the junction of Oxford Street and Regent Street, but could not say at this stage whether it was linked to the Foot Locker incident.
At the scene of the second stabbing - on the corner of Regent Street and Oxford Street - a pile of blood-soaked clothes could be seen. The area had been cordoned off while police carried out their inquiries.