A man is critically ill in hospital after being attacked by a group of up to six men "armed with baseball bats and knives", police said.
Officers were called by the London Ambulance Service to reports of a stabbing in Walworth, south London, at 5.22pm on Friday.
A 24-year-old man, who was believed to have been attacked in Nursery Row Park, was taken to hospital suffering from stab wounds.
The Metropolitan Police said there have been no arrests and a crime scene remains in place as the investigation continues.
Detective Sergeant Rob Merrett, of Central South CID, said: "I believe the victim was attacked by a group of up to six males armed with baseball bats and knives.
"An investigation is under way, including forensic analysis of the scene and of all available CCTV footage, in addition to house-to-house and other local inquiries.
"I urge any witnesses, anyone with information, and in particular people who have mobile phone footage of the incident, to come forward and speak with police if they have not already done so."
A Section 60 order was authorised for the Walworth area following the incident and additional patrols have been put in place.
Anyone with information that may assist the investigation have been advised to call 101, reference 5940/21aug.
