Roads have been closed, bridges washed out, people displaced and a state of emergency declared as the West Coast wakes up from what the mayor calls a "100-year" rain event.

While the deluge will lessen as it moves north, now a forecaster warns another "rain-maker" could be on the way for the North Island next week courtesy of ex-cyclone Trevor.

Torrential rain and strong winds have battered the West Coast region since Sunday night, with some parts receiving over 600mm of rain in the past 36 hours.

Yesterday the Waiho Bridge was taken out by rising and rough floodwaters of the Waiho River near Franz Josef.

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MetService meteorologist Micky Malivuk said this morning the centre of the system had moved north of Hokitika to Greymouth, and the heaviest rain this morning was forecast about north Westland and Buller.

Waiho Bridge has been
Waiho Bridge has been "completely destroyed". Photo / Supplied

The heavy rain should clear in the South Island by midday, before making its way onto the lower and central North Island.

Hokitika and Franz Josef were the hardest hit over the past 24 hours, both receiving 160mm, Malivuk said.

But higher up in the alps was where the real action was, with many stations receiving over 600mm since Monday night. Cropp River had recorded 630mm.

Waiho River in flood. Photo / Supplied
Waiho River in flood. Photo / Supplied

Westland Mayor Bruce Smith told Newstalk ZB last night heavy rain was at the base of their problems but people remain the focus of the council and Civil Defence.

"This is a 100-year event, there is a huge amount of rain … I haven't seen all of the rivers impacted in Westland at exactly the same time," he said.

Farmers on the south side of the Waiho River have already started to self-evacuate but the rising river was causing further headaches, Smith said.

West Coast Emergency Management Group said in a media update this morning over a dozen roads remained closed.

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Flooding at Harihari yesterday. Photo / Supplied
Flooding at Harihari yesterday. Photo / Supplied

These included the Waiho Bridge which had been completely destroyed, State Highway 73 due to a slip about Candy's Creek, and SH6 between Hokitika and Makarora.

Smaller sections closed included the road south of Haast to Jacksons Bay, South Turnbull Rd in Okuru, south end Arawhata Bridge for 200m, Hokitika Gorge carpark, road to Kokatahi, Sunset Point, and Hans Bay (Lake Kaniere) to Kokatahi via Dorothy Falls.

There were reported power outages in Awatuna, Kaihinu and Kokatahi.

The state of emergency was declared for the Westland District at 5.45pm yesterday.

Arawhata River in flood. Photo / Supplied
Arawhata River in flood. Photo / Supplied

The West Coast Emergency Co-ordination Centre (ECC) and Westland Emergency Operations Centre (EOC) were activated and aerial Inspections would take place this morning to assess the extent of damage.

Parts of Hokitika had been prepared to evacuate last night but this was not needed as water levels receded from the high tide.

So far seven people have been displaced from their properties in Waitoto, and the welfare centre at Haast has opened and accommodation for the displaced people organised.

Residents are advised to check their locals schools to confirm their status for Wednesday.

Malivuk said the system would weaken as it moved on to the North Island this afternoon but there could still be some heavy rain about Taranaki.

Meanwhile, WeatherWatch NZ said ex-cyclone Trevor, currently over Queensland, would drift east and join forces with a cold front in the Tasman Sea on Friday, sparking a new rain band and possibly a new low pressure system in the New Zealand area.

This could bring some rain to the North Island in the first few days of April.

Today's weather

Whangārei

Cloud increasing, chance shower from this morning. Northerlies. 25C high, 17C overnight.

Auckland

Cloud increasing, chance shower from this morning. Northerlies. 25C high, 18C overnight.

Hamilton

Cloud increasing, chance shower, more likely at night. Northerlies. 26C high, 16C overnight.

Tauranga

Cloud increasing. A few showers. Northerlies. 24C high, 18C overnight.

New Plymouth Cloudy with a few showers, turning to rain late afternoon. Strong northerlies, changing lighter southwest evening. 22C high, 13C overnight.

Napier Cloud increasing, with a few showers at night. Gusty northwesterlies, easing at night. 28C high, 17C overnight.

Whanganui Cloud increasing, with rain from evening. Gusty northwesterlies, dying out at night. 24C high, 13C overnight.

Wellington A few showers, turning to rain afternoon, briefly heavy, clearing evening. Gale northerlies, easing late afternoon, changing southerly overnight. 20C high, 14C overnight.

Nelson Rain, easing early afternoon then becoming fine. Northwest, strong at first, turning southwest at night. 21C high, 13C overnight.

Christchurch Occasional morning rain, then fine spells. Northerlies easing morning, afternoon southerly change. 23C high, 12C overnight.

Dunedin Fine spells. Chance shower, mainly around the middle of the day. Southwesterlies developing around midday, briefly strong. 19C high, 9C overnight.