Tourists taking holiday snaps along London's busy Oxford Street could hold pivotal evidence to the stabbing of a 22 year-old-man who died after being attacked, police said today.

The victim, who has not been named, was murdered yesterday outside a McDonald's restaurant during the afternoon rush hour.

Police said the man had became embroiled in a fight with an unknown number of attackers.

He was stabbed on the pavement in front of hundreds of shoppers who had jammed into the area near Oxford Circus underground station, shortly before 5 p.m.

Paramedics tried to revive him at the scene. He was taken to hospital but later died.

Detectives from the Metropolitan Police's Homicide and Serious Crime Command have since launched a murder inquiry.

A bloodied four-inch knife was recovered nearby and CCTV footage seized.

"This attack took place at a peak time in one of the busiest streets in London," said Scotland Yard Acting Detective Chief Inspector Bob Mahoney.

"We are very keen to speak to anyone who was in the Oxford Street area at the time of the incident who either witnessed this violent attack or saw people running from the area."

Police were particularly interested in tourists who may have been taking holiday snaps.

"We would be very keen to see these photographs as they could hold key information to our inquiry," he added.

A post-mortem was taking place this afternoon.

Knife crime has blighted London in recent months - the Oxford Street murder was one of several serious stabbings in 48 hours.

Two teenage boys were stabbed in Holloway on Sunday night while 16 year-old Jimmy Mizen was slashed in the throat at a bakery in Lee.