A man believed to be a window-cleaner is in a serious condition after falling from a building onto Oxford Street early on Tuesday.
Horrified commuters described seeing blood on the pavement after the man, in his mid-40s, fell from a height near Harewood Place.
Officers were called to the scene at around 6.30am.
London Ambulance Services and London's Air Ambulance attended the scene and the man was rushed to a major trauma centre at a central London hospital.
A London Ambulance Service spokersperson confirmed: “We were called at 6.24am today to Oxford Street to reports of a person fallen from height.
“We sent our Hazardous Area Response Team, two incident response officers, an ambulance crew and two single responders in cars to the scene. London’s Air Ambulance was also dispatched by car.
“We treated a man at the scene for head and leg injuries and took him to a major trauma centre as a priority.”
A spokesperson for the Metropolitan Police said: "Officers were called at 6.30am on Tuesday November 14 to Oxford Street near Harewood Place.
"A man in his 40s, believed to be a window cleaner, had fallen from a height."
The spokesperson said the Health and Safety Executive had been informed.
Dan Smallbone tweeted: "There's a lorry stopped on the pavement in Oxford Street, police all around it and blood on the floor."
#oxfordstreet There is a lorry stopped on the pavement in Oxford street, police all around it and blood on the floor, it's definitely the aftermath of something maybe just a crash but nothing on the news... Anyone have a clue?— Dan Smallbone (@DanSmallbone) November 14, 2017
Another Twitter user with the handle @AlexScottlrv posted: "Guy fell off the building (window cleaner) alive but badly injured."
A different user said they "saw the ropes" from the window cleaning equipment.
The Met said the surrounding roads would remain closed while emergency services deal with the situation.
Spencer Jones, an accountant, told the Press Association the incident occurred outside the New Balance shop about 200m (656ft) from Oxford Circus station.
The 46-year-old said: "I didn't witness the accident, I got off a bus and walked past. There was a 7.5 tonne lorry parked up on the pavement, lots of clothes and a suitcase all scattered behind the lorry.
"There was quite a bit of blood around the back of the lorry."