Four people have been killed in the worst school shooting in Canada in almost 30 years.

2 others have been critically injured after a gunman opened fire on teachers and pupils at La Loche Community School in Saskatchewan province.

It's understood the suspect is a former student, who has been arrested.

Canadian Prime Minister Justin Trudeau says it was "every parent's worst nightmare".

Barry Brown is a journalist in Toronto and says police are investigating a motive: