The Metservice has issued an orange heavy rain warning for Westland south of Otira, the headwaters of the Canterbury and Otago lakes and Fiordland.
An orange strong wind warning is also in place for Marlborough, Canterbury, Otago, Fiordland, Southland and Stewart Island.
Meanwhile, Fire and Emergency NZ crews and a helicopter were called in to fight a scrub fire in the North Loburn White rock area about 12.30pm on Monday.
Residents reported seeing a large amount of smoke in the area. The helicopter was grounded at the scene due to high winds.
Metservice says it recorded a gust of 107km/h this morning. It has only exceeded gusts of 100km/h seven other times.
And strong wind gusts in Dunedin have caused trees to fall and block roads including outside a high school this afternoon.
Emergency services were sent to Highgate in Roslyn this afternoon after a tree fell at Columba College and there was a strong smell of gas.
Highgate is closed between Oban St and Pacific St.
More than 500 properties in Canterbury were left without power due to the severe weather.
This morning 398 homes in Coalgate, Glentunnel, Hororata and Whitecliffs lost power from about 6am, according to Orion. It was expected to be restored at noon.
Properties in Sheffield, Waddington, West Melton, Burnham, Ellesmere, Norwood and Springston were also without power at 10am.
Metservice is warning it is likely to be a "significant severe weather event".
"People are advised to keep up to date with the latest forecasts, as some areas could be upgraded to red warning."
Environment Canterbury has issued a flood warning for those near major alpine and foothill rivers, and is planning a response.
Parts of the South Island have also been battered with lightning strikes overnight and this morning.
Metservice reported there were 3424 strikes from midnight to 7am.
A fallen tree on the corner of Mill Rd and Oxford Rd. Photo: Facebook / Amy Roberts
Roads closures, warnings
Due to strong winds, motorists have been urged to use caution on a number of state highways.
Waka Kotahi NZ Transport Agency says there are strong wind warnings on the following roads:
• SH1 Rakaia to Timaru
• SH77 Methven to Windwhistle
• SH79 Fairlie to Geraldine
• SH80 Lake Pukaki to Aoraki Mt Cook
Caravans, campervans, high-sided vehicles and motor bikes should also be careful on SH73 Springfield to Arthurs Pass and SH8 Omarama to Fairlie.
The Haast Pass is closed due to fallen trees. SH94 Te Anau to Milford is also closed due to increased avalanche risk and is not expected to open today.
SH82 in Waimate was closed near the Hollands Bridge due to fallen trees but has sinsce reopened.
"Road users are advised to avoid the area or consider delaying your journey until this has been cleared," an NZTA spokesperson said.
MetService meteorologist Tui McInnes said the weather could become quite hazardous.
"That rain has to go somewhere and of course that rain drains into the rivers. Further to that, we've got the strong winds associated with this, which means it's good to be careful and keep an eye out because we're going to have some potentially quite hazardous conditions about for the next couple of days."
Increased runoff is expected to be pushed into alpine and foothill rivers.
Parts of the Ashburton River are expected to see water flows that will test flood protection works in the area.
ECan duty flood controller Chris Firth said while this weather is typical for this time of year, a combination of other factors will heighten its effects.
ECan is urging people in flood-prone areas to monitor the situation and move stock to higher ground.
By Devon Bolger and Star News
