Environment Canada is warning of near zero visibility and hazardous driving conditions in a fog advisory for most of southern Ontario and parts of northern Ontario.

The advisory says visibility may be significantly and suddenly reduced to near zero and says drivers should slow down, watch for tail lights and be prepared to stop.

It stretches through most of southern Ontario from Windsor and Chatham-Kent to Parry Sound-Muskoka, Bancroft and Kingston.

The advisory has also been issued for parts of northern Ontario, including Greater Sudbury, Manitoulin, Kirkland Lake and Elliot Lake.

Metrolinx is advising commuters to give themselves extra time this morning and to use caution in its parking lots, stairwells, and at GO Transit stations and platforms.

Anne Marie Aikins, Metrolinx's chief spokesperson, tweeted this morning that thick fog "could cause minor delays during (the) morning rush."