Three teenagers have been arrested on suspicion of murder after a 17-year-old boy was stabbed to death.
West Yorkshire Police was called at about 21:30 BST on Saturday to reports of a disturbance on East Park Road in the Ovenden area of Halifax.
Officers found two males with stab wounds and a third with a head injury. All three were taken to hospital for treatment.
Police said one of the teenagers, aged 17, died a short time later.
The other two injured teenagers are not thought to have life-threatening injuries. Both are in a stable condition.
Det Ch Insp Jim Griffiths said: "Inquiries are at an early stage and continuing, but we believe there were a significant number of witnesses to what happened."
Anyone with information should contact police on 101 or use West Yorkshire Police's live chat facility.
The three arrested teenagers remain in police custody.