(CNN)Five people are dead and an alleged shooter is in custody Friday after gunfire erupted at La Loche Community School in Northern Saskatchewan, Canadian Prime Minister Justin Trudeau said.

Two more people are critically injured, he said.

"Obviously this is every parent's worst nightmare," he said, calling it "a terrible, tragic day."

Clearwater River Dene Nation Chief Teddy Clark described the shooting as devastating in an interview with The Star Phoenix newspaper.

"Both Clearwater and La Loche, a lot of people are in shock. This is something that you only see on TV most of the time," Clark told the newspaper.

The school provides a prekindergarten to 12th grade education and houses about 900 students in two buildings, the school's Facebook page says.

Royal Canadian Mounted Police said "a serious incident" occurred at the Dene high school building, which was under lockdown Friday.

As a precaution, the Ducharme Elementary School was also under lockdown, the police said.

The school urged everyone to avoid the campus, according to its Facebook page.

"There is currently an emergency occurring at the Dene Building and we are asking the public to stay away while the matter is resolved by the RCMP," the school said on Facebook. "We will not be allowing anyone in or out until we have a clear idea of what is going on."

Royal Canadian Mounted Police and emergency personnel responded to the shooting, according to a Facebook post by Saskatchewan Premier Brad Wall.

"Words cannot express my shock and sorrow at the horrific events today in La Loche," he said. "My thoughts and prayers are with all the victims, their families and friends and all the people of the community."

Saskatchewan Education and Social Services will be providing crisis support and counseling services to the school and the community, the premier said.

5 die in shooting at La Loche school in Saskatchewan - CNN.com