The West Coast is being battered by thunderstorms, and motorists in the region are being warned to drive with extra care.
MetService said 60 to 80 millimetres of rain fell in some places overnight, and more was expected today.
Meteorologist Ravi Kandula said there was a low to the west of the South Island bringing wild weather to the north of the glaciers.
The low would mature and head north towards Buller and Nelson today.
Mr Kandula said a southerly front would reach Invercargill around midday, causing snow down to 800 metres around Arthur's Pass and 600 metres in parts of Otago and the Southern Lakes district.
"Once that front starts to move its way up the country, there's going to be reasonable amounts of rain and slush about on higher passes.
"So it's going to be advisable to make sure that people are carrying chains and doing all the usual, sensible things regarding winter weather driving," he said.