A man was stabbed to death in a fight outside a semi-detached house in north west London.
Police were called to tree-lined Chester Drive, Harrow shortly after 2am on Thursday.
Officers responded with London Ambulance Service who treated the victim in his late 50s.
Despite their efforts paramedics pronounced him dead at the scene, a short walk from North Harrow Tube station.
Another man, in his 30s, was arrested at the scene on suspicion of murder and has been taken into police custody.
Detectives are unsure if the pair were known to each other. They are working to inform next of kin, Scotland Yard said in a statement.
A Metropolitan Police spokesman said: “A crime scene is in place and enquiries are ongoing, led by the Specialist Crime Command.”
London Ambulance Service added: “We were called at 2.06am on March 16 to reports of an incident on Chester Drive, Harrow.
“We sent a number of resources to the scene, including two ambulance crews, an advanced paramedic, an incident response officer and a clinical team manager. We also dispatched London’s Air Ambulance by car.
“Our first medics arrived in less than four minutes.
“Sadly, despite the best efforts of our crews, a person died at the scene.”
Anyone with information, video or images should call police on 101, quoting CAD 523/16 Mar.