Heavy wind and rain alerts for many areas through Thursday

Heavy rains are on their way for a swathe of the South Island, including Canterbury and Westland, where forecasters say up to 160mm could fall, with strong winds also expected for some places.

From Thursday morning into that night, MetService said those in Canterbury - particularly at the headwaters areas of the Canterbury lakes and rivers and the Westland ranges, should expect heavy falls.

And orange weather warning had been issued: "Expect 120 to 160mm of rain about the main divide, and 60 to 100mm within 20km farther east."

Peak rates could reach up to 30mm an hour around the middle of the day.

The downpours could cause surface flooding, create difficult driving conditions and cause waterways to rise rapidly, particularly in low-lying areas.

Those in the Canterbury High County should also expect severe gales, gusting up to 120 km/h in exposed places, which could cause damage to trees and powerlines, and also affect driving - particularly for motorbikes and high-sided vehicles.

Yellow weather watches

A heavy rain watch was also in place for: The ranges of the Buller and Grey Districts, from Thursday afternoon into early Friday morning; for the headwaters of the Otago lakes and rivers, for Thursday; and for Fiordland north of Doubtful Sound, for Wednesday night into Thursday morning.

And strong wind watches were issued for the Wellington Region, including the Wairarapa, and for the Marlborough Sounds, for the period from Thursday night into early Friday morning. Forecasters warned that those northwest winds could approach severe gales in exposed places.