A gang riding mopeds ploughed down a tourist and broke his leg as they attempted to steal his watch.
The victim, in his 30s, was on holiday in London when he was pursued by the group on Park Lane in Westminster, the Metropolitan Police said.
CCTV footage shows the man running away after he was surrounded by eight suspects on four mopeds - three of which mount the pavement as they pursue him.
He is seen escaping from the group but falls to the floor moments later after being struck by one of the vehicles.
The man was able to crawl away from his attackers, who rode off empty-handed, but he required treatment for a broken leg, Scotland Yard said.
Police are appealing for information about the attack which happened at 3.10am on April 30.
Detective Constable Richard Kidd said: "This happened just after 3am when a group of four or possibly more mopeds riding together would have been conspicuous.
"I want to hear from anyone who recalls seeing such a group or who may have seen the mopeds being abandoned - or perhaps being stored in a lock-up or similar location - in the early hours of April 30.
"One of the mopeds would have sustained damage to its left side."
Anyone with information should contact police on 101 or Crimestoppers anonymously.