Two people were seriously injured in a collision in Richmond Hill Sunday afternoon.

York Regional Police said the crash happened on Stouffville Road between Yonge Street and Bayview Avenue around 2 p.m.

Four vehicles were involved in the collision, police said, and two people were transported to the hospital with serious injuries.

It is not known what caused the crash and whether snowy conditions were a factor.

The Greater Toronto Area is under a winter weather travel advisory as a significant snowfall blanketed the region Sunday.

Environment Canada said some areas have seen five to eight centimetres of snow in the morning.

The agency noted that two to five centimetres of snow is expected to fall in the afternoon and evening.

Ahead of the snow, motorists were urged to plan their travel and exercise caution due to “hazardous winter driving conditions.”

Earlier Sunday morning, a 27-year-old woman was taken to a hospital with serious, life-altering injuries after a crash in Markham.

Ontario Provincial Police said it happened on Highway 404 near 19th Avenue just after 9:30 a.m.

A vehicle lost control and collided with a tow truck that responded to an earlier crash on the highway, the OPP said.

“Roads were wet with poor visibility due to snow falling,” the OPP said in a tweet.

The snow is expected to taper off Sunday evening.