State Highway 73 between Springfield and Otira, including Arthur’s Pass, is expected to remain closed throughout Thursday morning as crews work to clear heavy snow from the route.

NZ Transport Agency said between 15 and 25 centimetres of snow had fallen from Porters Pass through to Craigieburn Cutting.

Roading crews were assessing conditions and monitoring how much more snow could fall before deciding when the highway could safely reopen.

Multiple rockfalls have also been reported in the area, and motorists are being asked to avoid the route or delay their journeys.

NZTA said a further update on the SH73 closure was expected around midday.

State Highway 94 between Te Anau and Milford Sound also remains closed from the Lower Hollyford Road intersection to Donne River because of the avalanche risk.

Based on current forecasts, that section of highway is expected to reopen between mid and late Friday morning.

Area warnings are in place for surface flooding on State Highway 6 between Haast and Fox Glacier, and from Lake Wahapo, near Whataroa, to Harihari.

The worst effects of the winter storm are expected to unfold across the South Island on Thursday.

People travelling through inland and alpine areas are being urged to monitor weather forecasts and check the latest highway conditions on the NZTA Journey Planner before setting out.