A man murdered in Oxford Street, Britain's busiest shopping district, was stabbed in a row after a drink was thrown, police said.

A post mortem examination is being carried out on Steven Bigby, 22, of north London, but "the early indication is that he died from a single stab wound to the chest", according to the Metropolitan Police's acting Deputy Chief Inspector Bob Mahoney.

The murder took place after two groups of black men clashed in London's bustling Oxford Street outside a McDonald's restaurant at around 4.45pm on Monday.

Detectives are hunting four black men aged between 20 and 30 who fled the scene.

Forensics officers search the stabbing scene in London's Oxford Street Full Image

Mr Mahoney said that at the moment police were treating it as a "spontaneous incident" and there is nothing to suggest it was gang related or linked to any other crime.

One of the four men who fled was wearing a red t-shirt, another was wearing a white t-shirt, the third was in a vest and muscularly built while the fourth was dressed in dark clothing.

There were four people in one group and at least three people in Mr Bigby's group.

Mr Mahoney said: "Two groups of black men came together. A drink was thrown. The incident escalated very quickly and Steven was fatally stabbed.

"There is a possibility that the four men were walking up and down on Oxford Street during the afternoon. It is possible they may have been seen promenading."

Forensic tests are being carried out on the knife which was recovered at the scene. Detectives are trawling through hundreds of CCTV images.