A man has been stabbed to death near Oxford Street in central London.
The emergency services were called to the scene at about 11.40am on Monday to reports a man had been found with stab wounds.
Police officers, paramedics and an air ambulance arrived at Poland Street but the victim was pronounced dead 40 minutes later, the Metropolitan Police said.
A man has been arrested in connection with the incident, the force added.
The victim has not yet been identified.
The London Ambulance Service said the first paramedic arrived at the scene in less than seven minutes.
"Despite the best efforts of our teams, the patient sadly died at the scene," it added.
The killing marks the 57th homicide in London so far this year.
Poland Street is a turning off Oxford Street, which is one of the busiest shopping areas in Europe and attracts tens of thousands of visitors a day, and runs into Soho, another busy area known for its nightlife.