A gunman killed four people and critically wounding several others on Friday in Canada's worst school violence in years.
The suspect first shot his two brothers at home before opening fire at a high school in the western province of Saskatchewan, a family friend and the town's acting mayor said.
"Obviously this is every parent's worst nightmare," said Prime Minister Justin Trudeau, who initially reported five people were killed. He was in Davos, Switzerland, for the annual World Economic Forum.
Officials have not given a motivation for the shooting which occurred at a high school called the Dene Building in La Loche, a remote northern aboriginal community about 600 km (375 miles) north of the city of Saskatoon. Police said a suspect was arrested after the shooting.
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.
He also told the Associated Press that his 23-year-old daughter Marie, a teacher, was shot to death.
Witnesses reported seeing a "boy," opening fire inside the building, who was either a student or formerly attended the school.
Community gathering to say a prayer outside of school where people were shot in la loche. pic.twitter.com/liKvMQEyrI
— Sarah Plowman (@SarahPlowmanCTV) January 23, 2016
Several students said they heard six or seven gun shots at around 1:00 pm (1900 GMT).
"I ran outside the school," La Loche student Noel Desjarlais told Canadian media.
"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."
Police apprehended the suspect outside the school and seized a gun, but have not yet released the identity of the shooter or victims.
Chief Bobby Cameron of the Federation of Saskatchewan Indian Nations said a teacher and a teacher's assistant were among the four killed, while a few students were in surgery in Saskatoon.
A family friend, Joe Lemaigre, said the teenaged suspect first shot his two younger brothers before heading to the school.
"After he shot his two brothers, he walked back to school and he shot ... a teacher and a girl. They're both dead. Four of them died," he said.
Although mass shootings are rare in Canada, which has stricter gun laws than the United States, the school shooting is Canada's deadliest in 26 years.
In 1989, 14 college students were killed at Montreal's Ecole Polytechnique and a shooting in 1992 at Concordia University in Montreal killed four.