Possible tornado rips through Westland as severe weather affects much of South Island

Some businesses in Greymouth have been damaged after a possible tornado tore through the West Coast town late last night.

Severe weather forecasters are investigating the possible tornado as wild weather affects much of the South Island.

Paula McCobb of Honda Farm, Trail and Road said they got a call from police late last night after their Tainui Street business was hit.

They got into town before midnight to assess the damage and begin the clean up.

"We found three smashed windows. One where a big branch, or a big piece of wood, had gone through it, through the door.

"We found a lot of debris around everywhere, on the roads."

McCobb said the shop was open as usual and they are grateful for the community that has rallied around to support them.

MetService has reduced its severe weather warnings from 19 to seven.

Strong wind and heavy rain warnings have been in place for Dunedin and the eastern Southland coast.

The regions were now clearing up after a stormy night and morning.

MetService meteorologist Amy Rossiter said 30 to 50 millimetres of rain had fallen across Ōtepoti in the past 12 hours.

Gusts of 142 kilometres per hour were recorded in exposed areas around Dunedin and Clutha.

A strong wind warning was also in place for Banks Peninsula until late tonight, along with a heavy rain watch for Canterbury.

Wellington had a heavy swell warning in place for tomorrow, with six-metre waves forecast.

Earlier today, Rossiter told Morning Report a front had moved through overnight, bringing a change from a very strong, warm and moist northwesterly flow to a southerly flow.

There was also a deep low off the east of the South Island that was driving stronger winds and heavier rain to the Otago and Southland regions.

Severe gales had been recorded overnight, with Rossiter saying Mount Hutt reached gales of 190kmh while Nugget Point reached 142kmh.

A front moved through Westland around 10.30pm on Monday night, causing a possible tornado.

"There were some signals on our radar that suggests there may have been a tornado. Our severe weather forecasters are still investigating that, but at this stage, it looks like there was a possibility of one."

Snow had also started to show, as it does in colder outbursts, on the Crown Ranges, Rossiter said.

Power outage in Otago region

Parts of Otago are without power after being buffeted by strong winds overnight.

Several roads around Dunedin's central city are also closed due to either flooding or trees downed by the storm.

26 millimetres of rain fell in central Dunedin between 5am and 10am this morning.

Gusts also reached 50kmh.

Power is out on parts of the Otago Peninsula as well as Dunedin's West Harbour.

Clyde, in Central Otago, is also without power, as are the South Otago townships of Clinton and Owaka.

In a statement, Clutha District Council said parts of the area were without power after the storm, and the outage would disrupt rural water schemes.

Contractors were on hand to restore it once power was reconnected, and crews were out checking for damage and clearing drains, the council said.

There was also widespread flooding on roads, notably on Kaitangata's main street and in Lawrence, it said.

Motorists were urged to drive to the conditions and slow down through flood waters.

Dunedin City Council said the bad weather arrived later than expected, about 5am on Tuesday.

Stormwater systems were coping well so far, with staff and contractors on standby if any issues came up, the council said.

Otago Civil Defence said drivers should take extra care, with tree branches likely to be down across roads and some traffic lights affected.

Motorcycles and high-sided vehicles should also take extreme care travelling in high winds on State Highways 1, 85, and 8, Otago Civil Defence said.