Shoppers looked on in horror as a man fell to his death from an escalator in Debenhams' flagship branch in Oxford Street.
Children were among those who saw the man fall in the department store at around 6.15 yesterday evening.
The man was pronounced dead at the scene, according to the London Ambulance Service.
One witness, who asked to remain anonymous, told the Standard: "I was there, but saw little and got out as fast as I could. It was horrible.
"From the fourth floor looking over the railings you could see people rushing around. [It was] not immediately clear what had happened but you could see staff looking worried and hurrying shoppers out of the way."
She added: "It was obvious something horrible happened.
"Decorative boxes for a Christmas display were scattered around and about 20 minutes later they said over the Tannoy the store was closing immediately."
Another witness told London24.com: "I heard a loud bang, commotion followed and a man was lying on the ground. I initially thought it was fireworks.”
A Met police spokesman said: "Police were called at 6:15pm to Debenhams in Oxford Street to a man who had fallen from an escalator.
"Police and London Ambulance Service attended and the man was pronounced dead at the scene."
The victim is yet to be formally identified and his next of kin have not been informed, Scotland Yard said.
A post-mortem is due to take place.
A London Ambulance Service spokeswoman said five other people were treated for shock, though none required hospital treatment.
Debenhams said in a statement: "Debenhams can confirm that police were called to the Oxford Street Debenhams store at 18.15 last night following a serious incident where a man fell from the third floor.
"At this stage there are thought to be no suspicious circumstances. Debenhams continues to work with the authorities on the matter."
