Grape growers in Marlborough, Nelson and other parts of the South Island are preparing for frost on Friday and Saturday mornings.

Up to a hundred helicopters from around New Zealand are being brought in to use their rotors to keep frosty air away from vulnerable vines.

Hundreds of wind machines will also be operating if the frost eventuates.

Marlborough grower Stuart Smith says there is strong competition for helicopters among South Island vineyards.

He says the frost-fighting helicopter service could cost growers $10,000 or more.

Mr Smith says grapes are at the so-called influorescence stage, with berries not yet formed. He says they are particularly vulnerable and cannot handle much frost.