The South Island is set to be hit with a wave of severe weather bringing thunderstorms and a risk of localised tornadoes.

MetService has issued weather warnings for many parts of the south as a front moves across the country on Wednesday.

A severe thunderstorm watch has been issued for Nelson, Buller, Westland, the Canterbury High Country and Fiordland from 6am-3pm today.

The forecaster is warning there is a risk of thunderstorms bringing damaging wind gusts of more than 110 km/h and tornadoes.

"Wind gusts of this strength can cause some structural damage, including trees and power lines, and may make driving hazardous.

"If any tornadoes occur, they will only affect very localised areas."

Orange heavy rain warnings are in place for the Tasman ranges west of Motueka, Buller and Westland.

170mm to 250mm of rain is expected to accumulate around the ranges south of Otira, MetService says.

Heavy rain watches are in place for the Richmond and Bryant Ranges, the Rai Valley area and northern Marlborough Sounds as well as Mt Taranaki and the Tararua Range in the North Island.

Strong wind watches are in place for the Canterbury High Country, Wellington, Taihape, the ranges of Hawke's Bay, parts of Wairarapa, inland Marlborough and the Marlborough Sounds.

It follows a night of thunderstorms across the country on Tuesday.

There were 525 lightning strikes measured in the South Island and 115 in the North Island.