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.

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".

A total of 10 people have been arrested in connection with the murder, police confirmed.

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.