The biggest snowfalls of the winter so far could be on the way for Canterbury’s alpine passes and inland state highways next week.

The New Zealand Transport Agency is urging motorists to plan ahead, with snow expected from Sunday and the heaviest impact likely on Monday and Tuesday.

Forecasts supplied to NZTA show up to 20 centimetres of snow could fall around Porters Pass on State Highway 73 and Lewis Pass on State Highway 7 on Monday.

There is also a risk of more than 10 centimetres of snow between Burkes Pass and Lake Tekapo in the Mackenzie Basin on Tuesday.

NZTA said the conditions could lead to state highway closures or restrictions, particularly for people travelling home across the South Island after Saturday night’s All Blacks-France rugby test in Christchurch, or heading away for school holiday trips.

MetService has also issued heavy rain and strong wind warnings for parts of the South Island.

Orange heavy rain warnings are in place for Fiordland, the headwaters of the Otago lakes and rivers, the ranges of Westland, and the headwaters of the Canterbury lakes and rivers south of Arthur’s Pass.

NZTA said heavy rain could cause streams and rivers to rise rapidly, with surface flooding, slips and difficult driving conditions possible.

The Canterbury high country is also under an orange strong wind warning from 3am tomorrow, with severe northwest gales forecast to gust up to 130 kilometres per hour in exposed places.

Drivers are being urged to carry warm clothing, water and food in case they become stuck or need to wait for conditions to ease.

NZTA said motorists should also make sure they have enough fuel or battery range in case detours or diversions are needed.

In heavy rain, drivers are advised to slow down, increase following distances, avoid sudden braking, use headlights during the day, and avoid driving through floodwaters where the depth is unclear.

People driving high-sided vehicles, towing vehicles or riding motorcycles are being urged to take extra care in severe gales.

Motorists can check the latest highway conditions and restrictions through NZTA’s Journey Planner.