An 18-year-old has been named as the suspect in a shooting that killed eight people and injured dozens more in British Columbia, Canada.

Police said Jesse Van Rootselaar was found dead at the scene from a self-inflicted gunshot injury. The motive for the attack is not yet known.

Six people were killed and at least 25 others were injured at Tumbler Ridge Secondary School. Two others - the suspect's mother, 39, and step-brother, 11 - were found dead at a nearby home.

Authorities said Van Rootselaar was born a biological male but identified as a woman.

"I can say that Jesse was born as a biological male who approximately six years ago began to transition to female," Dwayne McDonald, the Royal Canadian Mounted Police (RCMP) deputy commissioner, said.

The shooting at the nearby home occurred first, then the suspect went to the school, McDonald said.

The victims at the school were a 39-year-old female educator, three female students, all aged 12, and two male students, one aged 12 and the other 13.

Authorities do not believe there are other suspects involved in the shootings.

Police said they had attended the suspect's family home on multiple occasions over the past several years, with some calls related to mental health concerns.

Van Rootselaar previously had a valid gun licence that had since lapsed, McDonald said.

Police said Van Rootselaar had dropped out of Tumbler Ridge Secondary School four years ago.

Around 13:30 local time (20:30 GMT) on Tuesday, police received a report of an active shooter at Tumbler Ridge Secondary School. Officers arrived on the scene within two minutes of the call, heard active gunfire and entered the school, McDonald said.

Within minutes they located the shooter, who was deceased from what police say was a self-inflicted gunshot wound.

Authorities found two firearms - a long gun and a modified handgun - on the scene. But McDonald said it remains unclear the exact roles the firearms played in the shooting.

Police then began searching for victims throughout the school. Two victims were taken to hospital by air ambulance and remain in hospital.

Tumbler Ridge has about 2,400 residents, and its secondary school has 160 students in Grades 7-12.

Canadian Prime Minister Mark Carney said the students and teachers "bore witness to unheard of cruelty" during the shooting, noting that some victims remain in hospital "fighting for their lives".

Tumbler Ridge Mayor Darryl Krakowka told CBC that the community is small and tight-knit, and that he expected the victims to all be people he knows.

"I will know every victim. I've been here 19 years, and we're a small community," he said, after emerging from the town hall when the shelter-in-place order was lifted.

"I don't call them residents. I call them family."