Cromwell resident Jade McLellan said what she thought was a tornado picked up her father's 9-metre boat off a trailer and flung the two-tonne vessel over the neighbour's fence about 11am.
"We had a big gust of wind come through which picked up the neighbour's trampoline and spun that above fence level. Then we saw the boat flip up off its trailer and into the next door neighbour's yard. Now it's quite demolished," she said.
Neighbours had seen what they thought was the funnel shape of a tornado approaching their house about 11am.
"The wind really picked up and was throwing itself on the house and mum was yelling at everyone to get into the lounge. As I came through the hallway I looked through the sliding door and saw the boat flipping. It's quite crazy," Ms McLellan said.
Fire Service southern region operations manager Chris Munro said the South Island's firefighters had been very busy with weather-related calls today.
"We've got multiple calls at the moment: trees down, powerlines down, grass fires caused by the powerlines, trees down across the road."
Firefighters were also called when a house in Fox Glacier township caught fire after being struck by lightning around midday.
It was out by the time crews arrived, Mr Munro said.
The majority of calls were from Otago and Canterbury but there were also some small jobs on the West Coast due to heavy rain.
Dunedin police said motorists travelling between Oamaru and Dunedin should take extreme care as severe winds battered Otago's east coast.
They were attending two traffic incidents on State Highway 1, including a truck which overturned due to heavy winds.
The driver received minor injuries.
Air New Zealand said a number of flights to and from Queensland and Dunedin had been diverted or cancelled.
Affected passengers were being accommodated on other air services or by road, the airline said.
MetService said the front was expected to reach the lower North Island tomorrow night and clear the upper North Island overnight Thursday.
A brief burst of heavy rain was also expected to affect the Tararua Range, Mount Taranaki and the North Island central high country late tomorrow and early Thursday.
"This is a significant amount of rain and people in the affected areas are advised that rivers are likely to rise rapidly with the risk of flash flooding," the MetService warned.
Northwesterlies were expected to reach severe gale-force for most eastern parts of the South Island and Fiordland, as well as in Wellington and the east of the North Island.
Gusts could reach 140km/h in parts.
"Winds of this strength are likely to bring down trees and powerlines, and make driving dangerous, especially for motorcycles and high sided vehicles."