A 17-year-old youth has been knifed several times in what police have described as a brutal attack.
The teenager was attacked near a park in the St George area of Bristol during the early hours.
He was taken to an undisclosed hospital with life-threatening injuries, and remains in a serious condition in intensive care.
Crime scene investigators are searching Foxcroft Road, where the attack took place, for clues.
A spokesman for Avon and Somerset Police said: "This was an extremely serious assault which has left a teenager with life-threatening injuries.
"At this stage we're unsure what the motive was behind the attack and we would appeal for anyone with information to come forward."
A mystery caller is believed to have phoned for an ambulance after the attack, which happened at 0230 GMT.