A head-on collision between an SUV and a tractor-trailer has left a 61-year-old mother from Barrie, her 37-year-old adult son, and his nine-year-old son dead, according to police.

Emergency crews responded to a call at around 4:30 p.m. on Yonge Street south of 14th Line in Bradford, South Simcoe police said.

Police said when emergency crews arrived at the scene they found that an SUV travelling north had been involved in a crash with a tractor-trailer travelling south. Two of the SUV passengers died at the scene, the third later died in at a local hospital.

The driver of the truck was treated at the scene, said police.

With a file from Osobe Waberi