Fog affected flights at Dunedin Airport for part of this morning, with one to and from Christchurch cancelled and others delayed.
Senior Sergeant Brian Benn, of Dunedin, said motorists should prepare for black ice on the roads in Otago and Southland.
Motorists needed to ''exercise extreme caution''.
''Remember to drive to the conditions and keep your speed down, as you never know when you may hit ice and potentially lose control of your vehicle,'' he said.
New Zealand Transport Agency senior network manager John Jarvis said the authority was anticipating ''very cold'' temperatures across Otago and Southland.
Drivers should expect ice and people who could start work later in the morning should do so.
''When driving, slow down and drive to the conditions. Many roads will be gritted, which also require slower speeds, and there is likely to be black ice in remote places, in shady areas and on bridges,'' Mr Jarvis said.
MetService meteorologist Brian Mercer said the coldest places in Otago and Southland today would be ''inland and sheltered'' areas and a lot were likely to be frosty.
Queenstown and Central Otago
The Queenstown district could expect hard frosts in the morning and cool temperatures throughout the day.
Watch for ice - especially on the Crown Range, through the Kawarau Gorge and between Kingtson and Queenstown, the Queenstown Lakes District Council advised.
Be cautious of a build-up of loose grit and take care on bridge decks and shaded spots.
The Alexandra to Raes Junction Road was affected by thick fog, while the road from Raes Junction To Willowbank had ice.
In Central Otago, there was a hard frost, with freezing fog and black ice reported in Ranfurly, particularly in Patearoa and Waipiata areas. Extreme care was advised.
Roads in Maniototo and Manuherika had been gritted due to ice.
Roads were mainly dry, with temperatures sitting around -5'C. Caution was advised in shaded areas and across bridge decks as these may be slippery.
State Highway 6 Haast To Wanaka was also affected by ice.
- Staff reporters
