Witnesses have described their horror at seeing a man plunge to his death at the Tate Modern.
The man, in his late 40s, fell 100ft from a balcony at the Members' Room onto the pavement below. He was declared dead at the scene.
A Scotland Yard spokeswoman said: "We were called at 5.55pm on Tuesday to the Tate Modern following reports a man had fallen from a balcony.
"Officers and the London Ambulance Service attended. The man, believed to be in his late 40s, was pronounced dead at the scene. Officers believe they know the man's identity but await formal identification.
"Next of kin are aware. A post-mortem will be held in due course. An inquest will open and be adjourned in due course. The death is being treated as non-suspicious."
She added that it would be for the coroner to determine whether or not the man had killed himself.
Members of the public enjoying the sun on the banks of the Thames were in full view of the incident.
Twitter user CathHannahx wrote on the site: "Seeing the guy who jumped off the Tate Modern has been the most traumatic thing I have seen."
She added that she had "no idea" why he had done so.
Another user, salmasaid, wrote that many believed the death to be a stunt, adding: "The shock made everyone, including us, think that this was not real and that this was some outrageous performance. It's really sad."
Members pay upwards of £60 a year and have access to the exclusive bar, which is being refurbished next year, and free tickets to all exhibitions at the gallery.
Current shows at the central London venue include a Damien Hirst retrospective and a new Turbine Hall artwork, a performance piece by Tino Sehgal featuring a team of people who walk among visitors chatting and chanting, which opened to the public on the day of the man's death.
A Tate Modern spokeswoman said: "Our deepest sympathies go to his family. The police are investigating the incident."
Scotland Yard said their inquiries were continuing.