MetService has issued a rare red warning for heavy rain on the South Island's West Coast, with "significant impact and disruption" expected in the coming days.
Red warnings are reserved for only the most extreme weather events where significant impact and disruption are expected.
The heavy rain warnings came into place for Westland and Buller on Tuesday morning until at least Thursday afternoon.
"In consultation with local councils, MetService has upgraded rain warnings for Buller and Westland to red rain warnings," the forecaster said.
"Slips and floodwaters are likely to disrupt travel, making some roads impassable and possibly isolating communities."
The persistent heavy rain was expected to cause slips and widespread flooding.
"This is expected to be a significant weather event, especially for places where soils are already saturated from recent rain," West Coast Emergency Management said in a statement.
"People are advised to keep up to date with the latest forecasts, as some other areas could be upgraded to a red warning and more areas may be added."
Neighbouring regions including Tasman west of Motueka and Marlborough Sounds have also been issued with orange heavy rain warnings.
"Surface flooding, culvert blockages, tree slides and landslips are possible and driving conditions may be hazardous," Marlborough roads manager Steve Murrin said on Tuesday afternoon.
"We ask drivers to please respect speed restrictions and any traffic management signage.
"Contractors are out today preparing the network to try and keep roads open however, due to the amount of rain forecast and the current conditions, road closures are likely."
The worst of the weather was expected between Wednesday and Thursday, NIWA said.
Buller District Council staff and contractors have been working hard on flood mitigation measures in Westport ahead of the extreme rainfall.
The Emergency Operations Centre was activated on Monday and is fully operational, while a state of emergency has been declared for the whole of the West Coast region. Residents in areas that have had previous flooding are urged to keep a bag packed in case they are asked to evacuate.
Buller Civil Defence Controller Douglas Marshall said locals would have noticed a lot of activity today to mitigate the risks of flooding in some of the low-lying parts of Westport in particular.
Heavy machinery has been creating additional bunds, more pumps have been set up and inflatable barriers are being installed to protect critical infrastructure including the airport, the hospital, telecommunications sites and the O’Connor residential home. Contractors have been checking that drains are clear and the flap valves are shut.
There were 12,000 sandbags available for residents today, and another 10,000 are being delivered Tuesday evening.
"We have taken the lessons from the last two floods and we have listened to what our communities have told us," Marshall said.
"We are planning for every eventuality based on the forecast, modelling of the impacts that rain will have on rivers, the risk of high waves to our coastal communities, and drawing on experience."
He urged people living in low-lying areas to make their own evacuation plans and keep a bag packed with clothing and essential medication for each member of their household. They should also plan for their pets.
MetService has also issued a warning of coastal swells up to 5 metres high, which would impact coastal communities. Civil Defence had already been in touch with residents in Buller's smaller communities to encourage local preparedness.
"The message for tonight is that we have been doing all we can to reduce the impact of flooding on people and property, but people also have to be aware of the risks and take action to keep themselves safe."
The Insurance Council of New Zealand (ICNZ) is urging those living on the West Coast to act now on the red weather warning.
"Yet again West Coasters, those in the Grey and Buller districts and upper South Island likely face major disruption with a typical month's rain expected to fall to Thursday evening. This brings with it an attendant risk of flooding," ICNZ chief executive Tim Grafton said.
"People should put their safety first, heed the advice of local civil defence and contact their insurer early if affected."
ICNZ has advised locals to first and foremost act on instructions of local authorities to keep themselves safe. However, if possible, there is a list of things residents can do to help reduce loss and damage from the weather event:
Move valuables and electrical items out of reach of potential flood water
Move your car out of flood danger, and avoid driving if you can in line with local advice
Check gutters and drains are clear of debris
In case of high winds, secure large items such as barbeques, umbrellas and outdoor furniture, turn trampolines upside down, and pack away smaller items
Check your emergency kit, check in with your neighbours and be prepared for possible power outages
"Contact your insurer early if you suffer flood or storm damage, especially if you need to make emergency repairs, which should only be undertaken if they can be done safely," Grafton said.
"It's also important to take photos of any damage or items that have been ruined.
"No matter the outcome, that the West Coast is once again under a red warning is very difficult for all involved. The Buller District, and Westport in particular, have had a particularly hard run since last July’s major flooding and our thoughts are with them."
