The New Zealand Transport Agency says very cold temperatures are forecast overnight in Southland, Otago, parts of Canterbury.

Senior Network Manager of NZTA John Jarvis says Otago and Southland people should be ready for icy roads overnight and Thursday morning.

He says it's looking at being the coldest night of the year to date with widespread very cold temperatures across the lower South Island.

The NZTA is taking the extra step of advising drivers to start work later in the day if possible.

Mt Cook dropped to -9 last night, and temperatures as low as -7 degrees are forecast tonight for a number of inland areas.