Carney said federal Public Safety Minister Gary Anandasangaree was on his way to the community of Tumbler Ridge, where at least 10 people died in one of the worst mass killings in recent Canadian history.
"We will get through this. We will learn from this," Carney told reporters, at one point looking close to tears.
"But right now, it's a time to come together, as Canadians always do in these situations, these terrible situations, to support each other, to mourn together and to grow together."
Carney, who has postponed a trip to Europe, said he had ordered flags on all government buildings be flown at half-mast for the next seven days.
He is due to make a statement to parliament at 2pm on Wednesday.
Several prominent world leaders sent messages of condolence.
King Charles, Canada's head of state, said he was "profoundly shocked and saddened" by the shooting.
"We can only begin to imagine the appalling shadow that has now descended across Tumbler Ridge," he said in a statement released by his office.
Police said the suspect, described "as female in a dress with brown hair," had shot dead six people at the school in Tumbler Ridge, a remote municipality with a population of about 2400 people in the foothills of the Rocky Mountains.
Two more people were found dead at a residence believed to be connected to the incident and another person died on the way to hospital.
A suspected shooter was also found dead from what appeared to be a self-inflicted injury, police said.
At least two other people were hospitalised with serious or life-threatening wounds.
The shooting ranks among the deadliest in Canadian history.
Canada has stricter gun laws than the United States but Canadians can own firearms with a licence.
"There's not a word in the English language that's strong enough to describe the level of devastation that this community has experienced," said Larry Neufeld, a local provincial legislator.
"It's going to take a significant amount of effort and a significant amount of courage to repair that terror," he told CBC News.
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