The coldest temperature recorded was -13.5 degrees at Liawenee in central Tasmania just before 5am on Thursday.
Thick fog blanketed parts of Victoria, including Melbourne, where temperatures dropped to -2.1C in Coldstream in the city's east.
Fog shrouds Flemington Road as commuters cross the tram tracks in Melbourne. (Diego Fedele/AAP PHOTOS)
Mount Wellington in Hobart fell to a low of -1.9C just before 7am.
A road weather warning remains in place across much of Tasmania due to dangerous conditions created by icy roads.
Drivers have been told to be on alert in the North West Coast, Central North, North East, Central Plateau, Midlands, East Coast and Upper Derwent Valley.
Bureau of Meteorology community information officer, Brooke Pagel, said temperatures on the ground on Thursday morning may have been even colder than official figures, with the 'feels like' temperatures often recorded as several degrees lower.
"Temperatures at ground level can be many degrees lower than those recorded by standard weather stations, especially in these calm conditions with very clear skies," Ms Pagel said.
Milder conditions are expected on Friday morning, she added.
The bureau forecasts patchy morning fog and frost in Victoria and Tasmania on Friday with higher overnight temperatures.
3°C