By Rod Nickel

WINNIPEG, Manitoba (Reuters) - Five people were killed and two critically injured in a school shooting in a remote part of Saskatchewan on Friday and a suspect is in custody, Canadian Prime Minister Justin Trudeau said.

Trudeau did not give a motivation for the shooting in La Loche, about 600 km (375 miles) north of the city of Saskatoon. But La Loche acting Mayor Kevin Janvier told the Canadian Press the incident may have started at the suspect's home.

“I’m not 100 percent sure what’s actually happened but it started at home and ended at the school," Janvier said.

Mass shootings are relatively rare in Canada, which has stricter gun laws than the United States. With five dead, La Loche would be the country's worst school shooting since 14 college students were killed at Montreal's Ecole Polytechnique in 1989.

"Obviously this is every parent's worst nightmare," said Trudeau, who was in Davos, Switzerland for the annual World Economic Forum.

The shooting occurred in building that houses middle school and high school students, according to the Facebook page of the district, which has about 900 students.

Extra doctors and nurses have been sent to treat patients in Keewatin Yatthe Regional Health Authority's 16-bed hospital, said spokesman Dale West.

Teddy Clark, chief of the Clearwater River Dene Nation, said that his daughter told him about the shooting, the Canadian Broadcasting Corporation reported.

"We're just trying to pull together here and make sense of all this," Clark told CBC television. "It's not a very pretty scene right now."

La Loche student Noel Desjarlais told the CBC that he heard multiple shots fired at the school.

"I ran outside the school," Desjarlais said. "There was lots of screaming, there was about six, seven shots before I got outside. I believe there was more shots by the time I did get out."

A cellphone video taken by one resident and broadcast by the CBC showed students walking away from the school through the snow-covered ground and emergency personnel moving in.

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In 2014, a teacher expressed concern about violence at the La Loche school, citing an incident where a student who had tried to stab her was put back in her classroom after serving his sentence, and another attacked her at her home.

"That student got 10 months," Janice Wilson told the CBC of the student who tried to stab her in class. "And when he was released he was returned to the school and was put in my classroom."

(Additional reporting by Susan Taylor and Jeffrey Hodgson in Toronto and Martinne Geller in Davos, Switzerland; Writing by Lisa Shumaker; Editing by Grant McCool)