Motorists travelling across mountain passes are being urged to plan their trip and check to make sure roads are open.

Heavy snow is expected as low as 200 metres in Fiordland and inland Southland and MetService meteorologist Melissa Oosterwijk says lots of snow is expected on the Milford Road.

"We are currently expecting around 15 to 20 centimetres on the top of the road, which is a pretty good accumulation."

Milford Road was closed last night due to rising avalanche hazard.

There is a chilly day in store for the South Island with a cold front moving up the country, Oosterwijk said.

"Further north, in the parts of Otago and South Canterbury, the snow is lower at around 400 metres, so the heavier stuff is above 800."

She said coastal areas can expect heavy rain starting from around midday.