The teenage suspect in a mass shooting in rural British Columbia had been the subject of a number of police visits in recent years because of mental health issues, authorities say.

Police say the 18-year-old - who was found dead on the scene from a self-inflicted gunshot wound - killed eight people, including six children, in Tuesday's attack in Tumbler Ridge.

Jesse Van Rootselaar had previously been apprehended and assessed under the Mental Health Act, and used to have a firearms licence.

It is unclear who owned the guns used in the attack, or what was the motive. Prime Minister Mark Carney has said he will visit the mountain town in the coming days.

British Columbia, in western Canada, proclaimed Thursday a day of mourning across the province.