OTTAWA — Four people were killed and an unknown number were injured in a school shooting in a small town in northern Saskatchewan on Friday, the Royal Canadian Mounted Police said.

Chief Superintendent Maureen Levy told a news conference in Regina, Saskatchewan, that one male, whose age and name she declined to disclose, was in police custody and that a firearm had been seized.

She offered few details about the shooting, which began just after lunchtime, but she said that there was no further danger to people in La Loche, a remote community of about 2,600.

Prime Minister Justin Trudeau, apparently acting on incorrect information from the police, said that there had been five deaths when he spoke at an earlier news conference from Switzerland, where he is attending the World Economic Forum.

“We all grieve with the community of La Loche and all of Saskatchewan,” Mr. Trudeau said. “This is every parent’s worst nightmare.”

Georgina Jolibois, the local member of Parliament and a former mayor of La Loche, said in a statement, “The shooting hits close to home for me as my family members attend the school.”

She added: “The community of La Loche is strong and closely knit. We have faced adversity in the past, and we will persevere.”

The town’s acting mayor, Kevin Janvier, said that his daughter, Marie, a teacher at the school, was among the dead, according to The Associated Press.

The La Loche Community School has about 900 students in classes from junior kindergarten to Grade 12. A Facebook post by the school said that the episode had occurred in a building for Grades 7 to 12.

The local population is largely aboriginal Canadian. Hunting and fishing are popular activities in the area, and hunting rifles are relatively common.

It was the first school shooting in Canada since 2007, when a 15-year-old boy was killed in a Toronto high school.

Canada’s deadliest school shooting occurred in 1989, when a man killed 14 students at École Polytechnique, an engineering school in Montreal, then killed himself. The deaths of those students, all women, led to the establishment of a national registry for rifles and other long guns. The Conservative government, which was defeated in October, dismantled that registry over the protests of many police forces and provincial governments.