The lanes are expected to remain closed for at least the next four hours, police say. The incident involved multiple vehicles, with what appears to be fuel spilling onto the highway following the crash.
It is not clear at this time if anyone was injured.
The adjacent collector lanes are moving slowly, with falling ice pellets and slippery road conditions hindering traffic flow through the accident area.
Commuters on Highway 401 are also negotiating the tricky driving conditions. Two eastbound express lanes on Highway 401 at Allen Road are blocked after a collision in the left-hand lane.
The city has 100 snow plows ready to hit the roads if needed.
The return of winter
After a weekend of warm, spring-like conditions, the temperature fell from a high of 23 C Sunday to a high of -1 C on Tuesday morning, according to David Phillips, senior climatologist at Environment Canada.
"I think the feeling out there is that we didn’t deserve this. We’ve endured a lot," Phillips told Matt Galloway, host of CBC's Metro Morning.
It was the coldest winter Toronto has seen since record-keeping began in 1937. But, Phillips said, it is not unusual to see winter-like conditions return throughout April.
"In 76 years, we’ve only had two Aprils without snow in Toronto. So this is not something that is unusual, it is something we expect. Except we think we don’t deserve it," Phillips said.
Environment Canada has issued a special weather statement for the GTA, saying that "persons in or near this area should be on the lookout for adverse weather conditions and take necessary safety precautions."
The GTA could receive up to four centimetres of snow today, according to Environment Canada.
Pearson Airport is reporting normal operations this morning, but Air Canada is advising passengers to check their flight status before heading to the airport.