Strong winds, cold nights on way for South

New Zealand will get a "shock to the system" this week as temperatures drop around the country.

Much of central and southern New Zealand was on some form of weather watch or warning because of a low-pressure system making its way up the South Island, MetService meteorologist Andrew James said.

Strong wind warnings have been issued for nearly all of the South Island, with snow expected down to 700-800 metres.

Heavy rain warnings are in place for Buller, Westland and the Canterbury lakes and rivers headwaters, and a strong wind warning is in place for Canterbury high country, with expected gusts up to 120km/h in exposed places.

Road snowfall warnings are in place for Tuesday morning on Lindis Pass, Haast Pass, Crown Range Rd and Arthurs Pass.

It was expected to fall as low as 600m on some of those roads.

Overnight on Tuesday, temperatures in Christchurch and Ashburton are expected to plummet to -1 degC, with rain expected. But the sun will be back on  Wednesday, Thursday and Friday, with highs between 14-16 degC.