The teenager was attacked on St Margaret’s Avenue in the Horsforth area of Leeds, according to the head of a nearby school.
West Yorkshire Police said officers were called to the scene just before 3pm on Tuesday to reports of an assault.
The force said a teenage boy has been arrested over the incident.
Senior investigating officer Detective Chief Inspector Stacey Atkinson said: “Our investigation is at an early stage and we are carrying out extensive inquiries to establish exactly what led to this needless loss of a young man’s life.
“We understand the immense impact and huge shock a tragic incident of this nature will will have on the community locally.
“Our neighbourhood police team are working with partners, including schools in the area to offer support and reassurance.
“We have already spoken to a number of witnesses and are keen to hear from anyone who has information about the incident.”
Around half a mile from the police cordon on Church Road, about 50 young people were gathered on Tuesday night for a candlelight vigil on Broadgate Lane.
People could be seen hugging each other, with some wiping away tears, as they stood around a bench covered in floral tributes.
Two bunches of white flowers had also been left at a cordon on Church Lane.
Paul Bell, head of Horsforth School, said the boy who was stabbed is a former pupil.
In a message to parents, he said: “You will be aware of a distressing incident in the community today, involving a former student of Horsforth School who was stabbed on St Margaret’s Avenue.
“The police are aware and working with the school.”
Dr Bell said: “We are aware of the distress and upset this has caused students and staff who know the student.
“We will be supporting students and staff in school and will update you as soon as we are able.
“We have limited information at this time.”
A parent at the school, who did not wish to be named, said: “It’s horrible. It’s shocking because it’s a nice area. You read about these things happening in London and you think it’s dangerous to be a teenager there, but you don’t think it would happen here.
“I just keep thinking about the parents. He probably went out this morning and they were expecting him to come home, and he’s not there.”
A nearby resident, who did not want to be named, was picking her grandchild up from school when she saw the police cars and ambulance.
She told the PA news agency: “I thought it was a car crash at first.
“The school was very good, they messaged us to say they were keeping the children safe inside.
“I was very sad when I heard what had happened, it sounds like it’s a waste of two lives.”
Jonathan Pryor, deputy leader of Leeds City Council, said on X, formerly Twitter: “Heartbroken to learn to (sic) of a serious event in Horsforth this afternoon.
“I know the distress and upset this will cause students and staff.
“While there isn’t much we can say at this stage, an arrest has been made, and we will be supporting Horsforth School in every way we can.”
Published: by Radio NewsHub
Written by: Radio News Hub