Dense fog that has descended on much of southern Ontario, including the Greater Toronto Area, is posing hazardous driving conditions and affecting operations at airports.

Environment Canada has issued a fog advisory that stretches from Belleville, Ont., to Woodstock, Ont., and says there is near zero visibility in those areas.

The agency says drivers should slow down, watch for tail lights and be prepared to stop if visibility is reduced while driving.

Toronto's Pearson International Airport says the flow of arriving flights has been reduced to maintain safe operations amid the foggy conditions.

Billy Bishop Airport in downtown Toronto has also warned travellers that fog and poor visibility may cause flights delays.

The fog is expected to dissipate through the day.