Up to 30 vehicles are being towed out of state highways near Twizel and Aoraki Mt Cook as snow sets in.

State Highway 8 between Twizel and Fairlie and SH80 between Aoraki Mt Cook and Ben Ohau are closed due to the snow, police said, with vehicles needing to be rescued.

Wild weather has hit the South Island with emergency services already called to flooding and fallen trees.

Tasman District Command Centre Senior Sergeant Stu Koefoed said civil defence in Okarito was dealing with flooding at the lagoon and in Nelson there was flooding on Whakatu Dr although the road remained clear.

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At Golden Downs a tree was down and blocking both lanes of Kerrs Hill Rd.

Koefoed urged people to stay off the roads if at all possible with heavy rain due to lash the north and west of the South Island.

Rivers and streams could rise rapidly and driving conditions could become hazardous, he said.

"Stay safe. If you don't need to go out, don't. Stay at home out of the rain."