A head-on collision in Bradford,Ont. Friday afternoon has killed a Barrie woman, her 37-year-old son, and nine-year-old grandson, according to police.

Emergency crews were called around 4:30 p.m. on Yonge Street, south of 14th Line, after a crash between a tractor-trailer and an SUV.

Sgt. David Phillips said the SUV was travelling north when it became involved in a collision with the truck which was travelling south.

He said two people were pronounced dead at the scene.

Simcoe County Paramedics said one person was taken to a Newmarket hospital with life-threatening injuries. The person was later pronounced dead.

Phillips said all three were occupants of the SUV. The driver of the truck was treated at the scene.

The victims are a 37-year-old man from Newmarket, his nine-year-old son and the man's 61-year-old mother from Barrie.

He said the cause of the crash is still unknown.

Police have closed Yonge Street between 12th Line and 14th Line for investigation.