A man has died after entering the River Thames while being arrested by police.
Officers were flagged down on Kingston Bridge at about 22:30 BST on Friday, the Metropolitan Police said.
A "verbal altercation" involving a man and a woman known to each other was taking place and an allegation of theft was made, the force added.
Officers were in the process of arresting the man, but he had not been placed in handcuffs, when he entered the water, the Met said.
The force's Marine Policing Unit, the National Police Air Service, London Fire Brigade and the RNLI were all involved in the search for the man, who was believed to be in his 20s.
He was recovered from the water at about 00:30 BST and was treated by paramedics, but was pronounced dead at the scene, police said.
The man's family had been informed and the force had referred itself to the Independent Office for Police Conduct (IOPC), according to the Met.
Deputy Assistant Commissioner Laurence Taylor said: "My thoughts, and those of the Metropolitan Police Service, are with the friends and family of the man who has sadly lost his life following this incident.
"I fully appreciate the public will be very concerned. We of course share that concern.
"The Met's Directorate of Professional Standards made an immediate referral to the Independent Office for Police Conduct as is protocol in any incident in which a person comes to harm following police contact."
The IOPC said its investigators had taken initial accounts from the officers involved.
In a statement, an IOPC spokesperson said: "We have now begun the process of gathering and reviewing evidence, including footage of the interaction between officers and the man.
"Our thoughts are with the man's loved ones and all those affected by his death."
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Independent Office for Police Conduct
Metropolitan Police
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