Snow warnings are being issued for the Desert Road as an active trough spreads a bitterly cold southerly change across the country.

The MetService has issued a snow warning for the Desert Road, Rimutaka Hill Road, Lewis Pass, Arthurs Pass, Lindis Pass, Porters Pass and Milford Road.

Snow is predicted to fall to lower then 500 metres overnight on the Desert Road.

The MetService says from 6pm tonight until 3pm tomorrow, 10 to 15cm of snow may accumulate near the summit, with 5 to 10cm above 800m and lesser amounts to 500m.

'This dramatic southerly change will sweep northwards during Wednesday, covering much of New Zealand by day's end,” says media and communications meteorologist Dan Corbett.

'Snow is expected to gall to low levels about southern to eastern parts of the South and lower North Islands.”

He says snow is likely to cause disruption to traffic, especially about the higher level roads of both islands.