Motorists are being asked to carry chains as a blanket of snow and ice covers the Lindis Pass, from Cromwell to Omarama.
Earlier today, a slip made up of 800 cubic metres of rock and soil closed State Highway Six, near Murchison.
It was brought down by the heavy rain that has been lashing the upper South Island.
A further two slips, one in the Buller Gorge and the other on the main road between Westport and Greymouth, reduced roads to one lane.
In each of those slips over 500 cubic metres of debris was dumped on the road.
State Highway 63 at Renwick, near Nelson, and State Highway 94, Te Anau to Milford Sound, have now reopened.