In the Mackenzie Basin, Lake Tekapo and Mount Cook Village received about 25 centimetres of snow over 12 hours.

A heavy snow watch is in place for South Canterbury south of the Rangitata River until midnight tonight, with periods of heavy snow expected above 800 metres and amounts possibly approaching warning criteria. Lighter falls are possible down to 400 metres.

Icy conditions caused major disruption on State Highway 8, also known as Fairlie Tekapo Highway, about 6pm on Sunday, when around 12 vehicles and a large truck were involved in crashes. One vehicle left the road.

An orange heavy rain warning has been issued for Marlborough and inland Canterbury north of Lake Sumner, with forecasters warning of dangerous river conditions, flooding, slips and possible road closures.

The warning is from 4pm today until midnight tomorrow, excluding the Marlborough Sounds.

MetService said 150 to 200 millimetres of rain was expected about the ranges, with possibly 300 millimetres about the Inland and Seaward Kaikōura Ranges.

Nearer the coast, 60 to 100 millimetres of rain is likely during the same period.

Peak rainfall rates of 15 to 25 millimetres an hour are expected about the ranges tonight and tomorrow morning.

The freezing level is expected to sit around 1800 metres, with snow likely above 1400 metres.

MetService said there was a high chance the warning could be upgraded to a red warning.

The National Emergency Management Agency is advising people not to enter floodwaters and to avoid unnecessary travel.

Residents should be ready for communication and power outages and be prepared to self evacuate if they see rising water.

A heavy rain watch has been issued for inland Canterbury about and north of the Rangitata River.

That watch runs from noon today until noon tomorrow, with periods of heavy rain possible and amounts approaching warning criteria.

MetService said the rain would fall as snow above 1000 metres, likely reaching as low as 800 metres. There is a moderate chance the watch could be upgraded to a warning.

A strong wind watch is also in force for the West Coast south of Westport until 6am tomorrow.

Southeasterly winds may approach severe gale strength about exposed valleys, and forecasters say there is a moderate chance it could be upgraded to a warning.