Christchurch high school has paid tribute to an "absolutely fantastic young man" who died on his way to school.

Tom Fastier, 17, died while walking along Opawa Rd, near the corner of Ensors Rd, in Waltham about 8.26am on Tuesday. It was possibly because of a medical event.

In an email to parents, Cashmere High School principal Mark Wilson said Fastier was an "absolutely fantastic young man and student of our school".

"The shock and sadness of his loss will be felt across our whole school community.

"Our thoughts and prayers are with his family as they attempt to deal with this sudden awful loss."

A family statement said Fastier was a gifted young man.

"Tom was in good health. He was a year 13 student … involved in several music groups and a talented bass player, as well as being involved in local and national music groups and competitions."

Wilson said some of Fastier's close friends were taken out of class and informed of his death before the school held an assembly to notify his classmates.

"On hearing news of this sad loss people will grieve in different ways and at different times. During today students needing time out were able to see our school counsellors and access support from other staff."

A backpack could be seen on the footpath near where the teenager died.

Wilson said school counsellors would continue to be available for students.

"In our usual Cashmere way, please be considerate and supportive of each other over the next days as people deal with this tragic loss."

Police Detective Senior Sergeant Greg Cottam said ambulance officers started CPR when they arrived, but Fastier died at the scene.

Police said Fastier's death had been referred to the coroner.

Cottam said the teenager was not wearing a school uniform – Cashmere High year 13s wear mufti – but a backpack was found at the scene.

"At this stage we've had a pathologist come down to the scene and have a look. We're still unsure of what has actually happened. [It's] possibly a medical event, so there will be a routine coronial investigation at this stage."

He said there was nothing to suggest foul play.