Mainlanders should prepare for snow down to low levels this weekend.

The MetService today warned a very cold southerly airstream was expected to spread over the South Island on Saturday, with snow down to sea level in many areas of the South Island.

The snow was likely to get down to sea level in Fiordland, Southland, Clutha and Otago during Saturday morning and afternoon.

Canterbury could be in for snow to near sea level during the afternoon and evening.

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The snow would be heaviest above 500m and MetService warned it could accumulate down to 300m.

Transport could be disrupted, stock in exposed places could be distressed and trees and powerlines could be brought down, MetService warned.

Meanwhile, the North Island would experience unsettled weather on Saturday, with heavy rain in the north.

Very cold air would spread across the lower and central North Island on Sunday and further warnings of snow could be issued.