The police watchdog has launched an investigation after a man suffering a "mental health crisis" died after being restrained.
Officers were called to reports of a man attempting to get into back gardens of properties in Polsted Road, Lewisham, southeast London, at about 2.20pm on Friday.
The Independent Office for Police Conduct (IOPC) said officers reported that the 35-year-old appeared to be having a "mental health crisis" and that footage from body-worn cameras showed him agitated.
It said the man, who has not been named, was restrained at the scene while an ambulance was called.
Paramedics are said to have arrived by the time the man became unwell.
They took the man to Lewisham Hospital, where he died.
The man's next of kin have been informed. A date for his post-mortem examination is still to be confirmed.
"Our investigators have begun reviewing body-worn video footage obtained from all officers who attended the incident and are undertaking door-to-door enquiries in the area," said IOPC regional director Jonathan Green.
"My thoughts are with the man's family and friends and to all those affected at this time and we will look to issue more information when appropriate."
Detective Chief Superintendent Tara McGovern said: "Our thoughts are with the family of the deceased at this extremely difficult time.
"Where a person dies following contact with the police it is right and proper that police refer the incident to an independent body to review the circumstances surrounding the death, which happened immediately in relation to this incident.
More from London
"We are reassured to know that the deceased's family is being supported and we are offering support to the officers involved in the police response.
"We are, and will continue to, provide our full support and co-operation to the IOPC investigation."