Boaties and residents in coastal areas of Southland and Stewart Island are being urged to prepare for a storm predicted to produce six-metre swells, 150km/h gales and power cuts tonight.
"We want people to stay at home and indoors from about 10pm tonight until daylight tomorrow," Southland's Emergency Management manager Neil Cruickshank said.
He said each household should have torches and spare batteries as well as a battery-powered radio, as power cuts can be expected particularly in rural areas.
Southland's harbourmaster, Kevin O'Sullivan, is urging boaties along the southern coast from Fiordland to the Catlins, including Stewart Island, to check their moorings during daylight hours.
He says six-metre swells are forecast in Foveaux Strait, and Bluff harbour will be affected.
MetService has issued a severe weather warning for southern parts of Fiordland and Southland, including Stewart Island and the Catlins, and says around Stewart Island gales may reach 150km/h.
"Gusts of this strength can blow roofs off houses, bring down power lines, break large branches off trees and blow vehicles off roads," said MetService spokesman Dan Corbett.
Severe gale northwesterlies may also affect inland Canterbury and Marlborough from late today and Wellington and Wairarapa tomorrow morning.
The bad weather is coming from a low pressure weather system which is moving fast and deepening quickly.
Snow will also drop to lower levels across southern parts of the South Island as colder air spreads in behind the weather system.
"This is looking like a weather bomb," WeatherWatch.co.nz head analyst Philip Duncan said.
"It will have hurricane-force winds circling around it and the only good thing is that the centre of the storm itself looks unlikely to directly hit New Zealand but it will brush the South Island."
NZN