A woman has died after being crushed when two window frames fell from a building in central London.
It is understood she was hit by the wooden frames of a ground-floor window in Hanover Street, Mayfair.
A witness told BBC London the woman was eating her lunch when she was struck on her chest.
London Ambulance and police were called at 11:30 BST. The woman, believed to be in her 20s, was treated at the scene but was pronounced dead by paramedics.
End Quote An eyewitness
Her eyes were open and I saw her hand move and then I think I saw her last breath and then the light went out, she'd gone"
The building, 5 Hanover Square, is a multimillion-pound development comprising six floors of office space. The ground floor is in the process of being turned into an art gallery.
Scaffolding was removed from the outside of the building a few weeks ago.
Orla Wojtowitz said it "happened in a second".
"She was just passing and then she was suddenly lying on the pavement," she said.
Another witness, who did not want to be identified, said the victim saw the frame beginning to fall but could not move out of the way in time.
A delivery driver who made the 999 call following the incident said he and 10 other people helped to lift the concrete frame off the woman which had "flattened" her.
The man, who did not want to be named, said: "I heard this incredible loud bang, the guy next to me said 'what the hell is that?', pointing.
"I turned round and the frame was on the ground and I was hoping it was a coat underneath, but then I saw an arm.
"I realised it was a person underneath so I phoned 999. The operator asked me to go closer to the victim so I got off the back of my wagon and went over.
"Her eyes were open and I saw her hand move and then I think I saw her last breath and then the light went out, she'd gone."
He said ambulance crews arrived about a minute or two later.
"She was in exactly the wrong place at the wrong time."
Beverley Hazel, another witness, said she was on her way to work in nearby Conduit Street at 11:30 BST when she saw a young woman "half lying in the road".
"A man was saying to her 'can you hear me?' but I don't think there was any response. It had just happened," she said.
"Then there was a lady who said she was a doctor. She got on with doing CPR and I counted three minutes for her."'I was in bits'
Mrs Hazel, who lives in Kennington Oval, south London, said she believed the victim was hit by two "massive" wooden window frames, measuring about 10ft by 10ft (3m).
"She was very young and slight. I've got two daughters, one younger and one older than this woman. I was in bits.
"If it had been my daughter I would have wanted someone with her.
"I went back later to lay some flowers."
Golam Mortuza, who works in the nearby Eat sandwich chain, was on his break when the incident happened. He said paramedics tried to revive the woman for 30 minutes.
"Life is so difficult. She was walking around and then this happened. It could have happened to anyone."
The Health and Safety Executive is aware of the incident, police said.
London Ambulance said it sent two cycle responders, two ambulance crews and a hazardous area response team and an air ambulance to the scene.
Hanover Square has been closed between Brook Street and St George Street.
The 8, 25 and 55 bus routes have been diverted.