Heavy rain, severe gale northwesterlies, and snow are sweeping through parts of central and southern New Zealand, with more warnings expected in the coming days.

MetService has a strong wind watch in place for Canterbury, which is being battered by north-westerly winds that are causing precarious conditions for high-sided vehicles and motorbikes in exposed places.

State Highway 1 near Waipara is closed after a large truck blew over, blocking all four lanes, shortly before 11am.

Waka Kotahi says the truck is on its side just south of the turn off to State Highway 7, in the Lewis Pass and work is underway to move it.

Police say no injuries have been reported but drivers are asked to avoid the area while a path around the truck is established.

In North Canterbury, Mainpower says its fault team is working to identify the cause of an outage that has cut power to 2500 households.

Elsewhere, wind damage has cut power to more than 200 households near Motunau Beach Road and a fault with an electricity line is affecting more than 600 houses in Hanmer.

The Motunau Beach Road power cut should be fixed by late afternoon, Mainpower says.

An active front over the Tasman Sea will move northwards over southern and central New Zealand on Thursday.

MetService says this front will be preceded by a strong and moist northwesterly flow, followed by strong and cold west to southwesterlies.

Heavy rain warnings are in place for Buller, Westland and the headwaters of Canterbury lakes and rivers about and south of Arthur's Pass.

There are strong wind warnings for Wairarapa, Wellington, the Marlborough Sounds and Canterbury High Country.

Several parts of the South Island and lower North Island are also under rain, wind and snow watches.

Cold temperatures, snow to follow warm spell

MetService head of weather communications Lisa Murray told Morning Report the rain is mostly focused on the western side and the wind on the eastern side of the country.

Several places, including Napier and Dunedin, will have warm temperatures ahead of today's front, she says.

"But behind that front, there's going to be a significant drop in temperature."

Snow is also expected tonight for Fiordland, Southland, Clutha, Dunedin, Central Otago and Southern Lakes.

She says Napier and Hastings will be in the mid-20s.

But behind that front, Lisa says there will be a sharp drop in temperature.

She says Dunedin, for example, will be a maximum of 21 degrees Celsius on Thursday, but on Friday that will drop to only 8-9C, with an overnight temperature of 3C.

Waka Kotahi journey planner Nicole Felts urges extra caution on the road and expects wintery conditions.

She told Morning Report people may not be expecting snow down near sea level in places like Otago and Southland at this time of year.

"[We're] asking that people drive a bit slower than they normally would and make sure that they're accelerating smoothly, braking gently, taking their time if they do absolutely need to travel tonight."

She also urges caution for those driving in heavy rain or winds.

Cyclone Lola

MetService is also keeping an eye on Cyclone Lola.

Lisa says the cyclone has weakened as its remnant moves towards the Tasman Sea.

"Then when we get this cold air that's coming up, bringing the snow and the rain and the wind to us, meets that in the Tasman Sea on Saturday, and it sort of reinvigorates the energy of that storm."

She says a low is expected to come on to the country. Northland, Auckland and Napier are among those first expected to be affected.

-RNZ.