A winter storm that brought a mix of ice pellets, freezing drizzle, and snow to the GTA on Sunday caused numerous collisions and power outages.

Environment Canada said the mixed precipitation created "hazardous" conditions for motorists across southern and central Ontario.

The national weather agency previously said that some areas could see snow and ice pellet accumulations of between five and 10 centimetres. The winter weather travel advisory for the GTA ended on Sunday afternoon.

Several collisions were reported across the province, including a fatal crash in the Fort Erie-bound lanes of the QEW near St. Catharines. In Kingston, one person died and multiple people were injured after a multi-vehicle crash in the westbound lanes of Highway 401.

OPP Sgt. Kerry Schmidt said on Sunday evening that at least 400 collisions were reported on the GTA highways alone.

“About 400 People found out the hard way that going the speed they want to go was still too fast,” Schmidt said in a video update posted on social media.

He said police responded to about half of the collisions and the other half were dealt with by tow trucks and the drivers. 

"Today is one of those days… it doesn’t look terrible and that is the danger because when it doesn’t look completely treacherous, people are going to think that it is manageable and they can head out there. But with that freezing ice and those pellets coming down, it can freeze on contact and it can cause a complete skating rink," Schmidt said.

He told CP24 on Sunday afternoon that new collisions continue to pop up as OPP officers try to clear the backlog.

"Drivers (are) going too fast, losing control on the snow and slush on the on-ramps and off-ramps," he said. 

"We are seeing multiple single-vehicle crashes, spinning out and some serious crashes as well." 

He is asking drivers to give themselves extra time for the morning commute on Monday.

Officers responded to a 12-vehicle crash near Davenport and Avenue roads on Sunday morning and while Toronto police say road conditions in the area are "treacherous," so far no injuries have been reported.

Mark Mills, the road operations superintendent for the City of Toronto, said salt trucks and snow plows are out, adding that Sunday will be an “all hands on deck” event.

“For today, please avoid travel if possible. If you need to travel today, please plan ahead,” he said at a news conference on Sunday morning.

“If you drive, please slow down. Drive to the conditions of the roadway. Please give yourself time and space for our cyclists, pedestrians.”

Mills said the main goal of road operations today is to make sure that the sidewalks, streets, and highways are clear for the Monday morning commute.

“It is a test with these mixed precipitation events,” he said. “We will have to be diligently patrolling.”

At Toronto Pearson International Airport, freezing rain started to fall at around 8 a.m. and flight delays and cancellations have been reported.

Officials at both Pearson Airport and Billy Bishop Toronto City Airport are urging travellers to check their flight status before leaving the house today.

Metrolinx reported some delays on GO bus routes due to the messy conditions. The TTC said while there may be some delays on bus routes, subway and streetcar service is running normally.

Environment Canada also warned of strong wind gusts of up to 70 kilometres per hour, resulting in blowing snow and reduced visibility.

High winds were likely to blame for falling glass at a busy intersection in the Financial District early Sunday morning.

Fire crews were forced to shut down the intersection of King Street West and Yonge Street due to glass falling from a building in the area.

The inclement weather has also prompted officials in Burlington and Mississauga to cancel their respective Santa Claus parades today.

Approximately 6,000 Toronto Hydro customers in Swansea and south Etobicoke were without power for several hours on Sunday evening.

Power was restored to the majority of affected customers around 9:30 p.m.

The outage was caused by a large tree branch on a wire, Toronto Hydro said.

For the remaining customers, Toronto Hydro said power is expected to be back between 3 a.m. and 5 a.m.

About 65,000 Hydro One customers also had their power knocked out.