A man has been arrested on suspicion of murder after another man died with stab wounds, the Metropolitan Police said.
Officers were called by the London Ambulance Service at around 1.30am on Saturday to a critically injured man at a flat in Hicken Road, Brixton, south-west London.
The man, in his 50s, was taken to a London hospital with stab injuries and died a short time later.
Another man, also in his 50s, has been arrested on suspicion of murder and has been taken to a south London police station where he remains in custody.
Officers are in the process of informing the deceased’s family.
The force said a post-mortem examination and formal identification will be arranged in due course.
A crime scene is in place at the block of flats in Hicken Road and forensic examination is ongoing.
On Saturday afternoon, a Metropolitan Police car was parked at one end of the street with a forensic services van at the other end.
Police and forensic officers were seen on the landing outside a flat in Gale House on Hicken Road.
Neighbours Grace and Heraldo, who did not wish to give their surname, told the PA news agency they were woken by noise at around 3.30am on Saturday.
Heraldo said: “I asked my wife to check through the window and we saw a police car.”
Grace added: “We want to live peacefully.”
Charlotte Smith, also a neighbour, said she did not see or hear anything.
She said that before she spoke with the police she “didn’t even know there was an altercation”.
Police urged anyone with information or any witnesses to call 101 using the reference 503/11feb or to contact Crimestoppers anonymously.
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