Canterbury is set for two days of winds strong enough to damage powerlines, level trees and make driving difficult.
Near the Canterbury foothills gusts could reach 150kmh today and 130kmh tomorrow, MetService said.
"These wind gusts have the potential to damage trees and powerlines and create difficult driving conditions," MetService said.
It also warned of heavy rain today in Fiordland, the Westland Ranges from Otira southwards, and the headwaters of the Otago and Canterbury lakes and rivers from Arthur's Pass south.
Up to 120mm could fall over 12 hours in Fiordland and the Westland ranges, with significant falls spreading east into the headwaters.
"People in these areas should be aware rivers could rise rapidly and there is the possibility of slips and surface flooding," MetService said.
The New Zealand Transport Agency urged motorists heading to the West Coast and using Canterbury's alpine passes to take "extreme care".
Journey Manager Lee Wright said strong wind and rain could make driving difficult on State Highway 73, between Springfield and Arthur's Pass.
"Motorists should check conditions before travelling and avoid all unnecessary travel if conditions could make travel hazardous," Wright said.
Metservice meteorologist John Law said Aoraki/Mt Cook has recorded wind gusts in excess of 100kmh, while in Arthurs and Porters passes winds have reached 80kmh. He expects those gusts to strengthen this evening.
Rain was expected to continue to fall in the affected areas tomorrow, but not as heavily. On Friday rain was expected to become heavier again for a sustained period.
Law said Christchurch city could expect gusts of between 80 and 90kmh by 8pm tonight, but it was inland Canterbury that would bear the brunt of the gales.
He said winds wouldease later tonight, but pick up again tomorrow morning.
The weather system would bump temperatures up throughout Canterbury, with the region set to hit highs of between 16 and 19 degrees Celsius from today through to Saturday, Law said.
MetService warned of a high risk of thunderstorms along the western side of the South Island, with small tornadoes possible except in the most northerly part of the area.
- The Press