Snowfall warnings are in place for South Island alpine passes and a Heavy Snow Watch covers the Mackenzie Basin as a cold front brings snow and surface flooding to southern highways.

NZ Transport Agency said crews had been assessing snow on State Highway 6 between Lowther and Parawa in Southland on Wednesday, with grit trucks operating.

Surface flooding had also been reported on State Highways 96 and 99, and more recently on State Highway 1 in central Dunedin.

NZTA said no closures or restrictions related to the weather event were in place at the time of its update, but urged motorists to take care and drive to the conditions.

MetService road snowfall warnings cover South Island alpine passes from Wednesday through to Thursday, September 17.

A Heavy Snow Watch is also in place for Central Otago, Queenstown Lakes District and the Mackenzie Basin until the early hours of Thursday.

The conditions follow an earlier NZTA warning that snow could disrupt travel through the Mackenzie Basin and on State Highway 73, including Porters Pass and west of Arthur’s Pass village.

Heavy Rain Watches also apply to the ranges of the Westland District and the Buller District.

NZTA has advised people travelling through affected areas to carry warm clothing, food and water in case of delays, and ensure they have enough fuel or battery range for possible detours.

Drivers should adjust their speed and following distances in wet conditions and avoid driving through floodwater where the depth is unclear.