There are reports of flooding and snow on state highways in the lower South Island as a forecast cold snap hits the mainland.

NZ Transport Agency Waka Kotahi (NZTA) said roading crews had been out on Wednesday to assess snow on State Highway 6 between Lowther and Parawa in Southland, and grit trucks were in operation.

NZTA said surface flooding had been reported in places across State Highways 96 and 99. 

"Most recently, surface flooding has been reported on State Highway 1 in central Dunedin.”

As of 4pm on Wednesday no highway closures or restrictions were in place, but road users were being urged to take care and drive to the conditions.

MetService has multiple road snowfall warnings in place for the South Island’s alpine passes, and a general heavy snow watch is in place for Central Otago, Queenstown Lakes District and the Mackenzie Basin until early on Thursday.

Heavy rain watches have been issued for the ranges of the Westland District and the Buller District.

— Allied Media