The first significant snowfall of the season has resulted in a number of collisions on GTA highways this morning.

All eastbound lanes of Highway 403 were closed between Dundas Street and Winston Churchill Boulevard this morning following a collision involving a tractor-trailer but the highway has since reopened.

Southbound lanes of Highway 410 were also closed at Highway 401 in Mississauga this morning due to a jack-knifed tractor-trailer. Those lanes have also reopened.

Sgt. Kerry Schmidt said Ontario Provincial Police have responded to approximately 400 collisions over the past 24 hours on GTA roads.

In York Region, two people were taken to hospital this morning following a collision near Green Lane and Yonge Street in East Gwillimbury. One person suffered life-threatening injuries.

A snowfall warning issued for the Greater Toronto Area yesterday ended as snow transitioned to rain early Monday morning.

The weather is also impacting flights at Pearson International Airport this morning.

Approximately 100 flights have been cancelled at the airport so far this morning and travellers are advised to check their flight status ahead of time.

TTC and GO Transit services are operating relatively smoothly this morning, according to spokespeople for both transit agencies.

"Buses and streetcars can only travel as fast as conditions allow," TTC spokesperson Kadeem Griffiths told CP24 Monday.

City of Toronto winter maintenance crews worked through the night to clear major roads and highways and are currently working to clear residential streets.