Such violence is rare in Canada, which has strict gun control laws unlike in the neighbouring US.
Police say they do not know the motive of the 18-year-old shooter, who died from a self-inflicted gunshot wound.
Carney will attend a vigil in Tumbler Ridge in memory of the victims, and he invited leaders from all political parties to join him in the town, his office told AFP.
Near the school, a bouquet of flowers and stuffed animals were placed at the foot of a tree.
Yellow police tape surrounded the school buildings and a snow-covered volleyball court.
The Royal Canadian Mounted Police on Thursday named the victims, and some families have released testimonials about the slain children.
“Seeing you leaving the house with that beautiful smile while going to Tumbler Ridge High school was so refreshing,” the father of 12-year-old Abel Mwansa Jr said on Facebook.
“I saw a bright future, a leader, an engineer, also a scientist in you,” said the post written by Abel Mwansa Sr., who wrote that he was “broken” seeing his son’s body “lifeless”.
The family of 12-year-old Kylie Smith said in a statement: “Kylie was the light in our family… She was a talented artist and had dreams of going to art school in the big city of Toronto. Rest in paradise, sweet girl”.
‘Surreal’
Police said Jesse Van Rootselaar, a transgender woman, killed her mother and stepbrother before shooting dead six people at the town’s high school – a 39-year-old female teacher, three 12-year-old girls and two boys, aged 13 and 12.
The initial death toll was reported to be nine before being revised down to eight, with a young girl “fighting for her life,” according to British Columbia Premier David Eby.
Van Rootselaar, who dropped out of the school four years ago, was known to have mental health issues.
Nearly everyone in the town has a connection to one of the victims.
Hundreds gathered for a candlelight vigil Wednesday night.
At the Tumbler Ridge Fellowship Baptist Church, Pastor George Rowe recounted his experience in the hours after the shooting.
When the lockdown was lifted, he went to the community center to comfort those waiting for word about their children.
The environment was “surreal,” he told AFP at his sparsely furnished church office.
“Most of the folk who were there then were parents and siblings waiting to know whether or not (their) child is alive or dead. Like, how do you deal with that?”
Rowe’s neighbour was among the children shot at the school.
He recalled how he always saw the boy getting ready to go church.
“Those little things, you know, it’s not there anymore, it’s, it’s just not there,” Rowe said.
The tragedy ranks among Canada’s deadliest, following the 2020 Nova Scotia mass shooting which claimed 22 lives and led to a ban on many assault weapons.
Authorities are investigating Van Rootselaar’s previous interactions with police and health care providers.
Van Rootselaar held a firearms license which had lapsed, and weapons had previously been confiscated — but were subsequently returned.
Carney made an emotional address to parliament, saying “these children and their teachers bore witness to unheard-of cruelty”.
He described Tumbler Ridge as a town of miners, teachers and construction workers who represent “the very best of Canada: resilient, compassionate and strong”.