Two adults and an infant were killed when a minivan struck the back end of a tractor-trailer Saturday on Highway 401 near Trenton, Ont., police say.

The two-vehicle crash happened around 1:15 p.m. west of County Road 40 on the highway’s westbound lanes, according to a Sunday news release from Ontario Provincial Police.

Three people in the minivan, all from Laval, Que., were killed in the crash, OPP said.

A 25-year-old man and a 22-year-old woman were pronounced dead at the scene, while an eight-month-old child was pronounced dead in hospital.

A four-year-old child suffered serious injuries and was flown by helicopter to a trauma centre in Toronto, OPP said. The tractor-trailer driver was unhurt, police said.

An investigation is underway into the cause of the crash. Highway 401 westbound has since reopened.