Persistent fog with visibility near zero is expected to develop this evening and become widespread by midnight.
Environment Canada has issued the fog advisory for Newmarket, Georgina and northern York Region.
Fog patches over some parts of the region may cause reduced visibility, according to the advisory, with several reports of visibility of less than 200 metres.
Travel may become hazardous later this evening as a result of the dense fog, which may persist into the middle of Thursday morning.
If visibility is reduced while driving, turn on your lights and maintain a safe following distance.
