Environment Canada says near zero visibility was "expected or occurring" Sunday morning as the weather agency issued a fog advisory for Toronto.
"Patchy dense fog has developed and will persist into the morning hours," Environment Canada said.
"Visibility may be significantly and suddenly reduced to near zero."
Motorists were advised that if visibility is reduced while driving, turn on your lights and maintain a safe following distance.
Toronto was also under a rainfall warning which Environment Canada extended on Sunday morning. Drivers were told to watch for ponding of water on the roads.
