Residents on the West Coast are being warned not to return to their homes just yet, as the risk of flooding in the area continues.
Hundreds of homes have been evacuated amid fears the Buller River could burst its banks.
A deluge of rain has led to a state of emergency being declared for the Buller District, with the town of Westport now cut off by flooding and slips.
A voluntary evacuation order became mandatory overnight. Police say a few people chose to stay put but up to 700 households in low-lying areas have evacuated. The New Zealand Defence Force sent in personnel to assist with the evacuation efforts.
"We know you are keen to get home," Buller Emergency Management said on Facebook on Saturday morning.
"We ask people to stay away from their homes while the risk remains. We will let you know when it is safe to return home."
Buller Emergency Management said there was still a large amount of water in the ranges that would need to make its way down the Buller River.
Four welfare centres have been set up on higher ground. Fire and Emergency Response Coordinator Mike Bowden says they are ready for potential escalation anywhere in the upper South Island.
Sheree Cargill spent the night in an evacuation centre at Westport South School.
"I was about to go to bed about midnight and there was knocking on the windows and doors and it was like what's going on?" she told Newshub.
"And Civil Defence, fire and police were all out there and said we had to evacuate now."
Cargill said about 160 people came through the doors of the evacuation centre between 12-4am, with some residents "pretty shaken up".
"There were lots of worried people who came here last night."
Despite the hardship she said the community and Civil Defence had rallied together to help each out.
"We've got a great community, great support," she said, encouraging people in the region to "have a chat to your neighbour, make sure everyone's okay and look after each other".
Buller District Mayor Jamie Cleine says local crews have been joined by reinforcements from out of town.
He said on Friday the Buller River was currently running at a 50-year flood level - and it is tracking towards a one-in-100-year event.
"The key risk area is overnight, so with the river already running high, we've got another 200-280mm of rain forecast in the next 36 hours - so it's highly likely that the river will continue to rise."
A high tidal surge was expected at 3:35am Saturday, Stuff reported.
Heavy rain is expected through Saturday, MetService saying a "large chunk" would come before midday and issuing a 'red warning' for the region, which is "reserved for the most impactful weather events".
"Heavy rain, with a chance [of] thunderstorm from afternoon, easing tonight," MetService said for Westport on Saturday morning. "Strong northerlies, gale gusting 110 km/h, tending lighter northwest this morning."
Nelson to the north has strong wind and heavy rain warnings in place.
"Rain with heavy falls, easing during the evening. Strong northerlies, gale gusting 100 km/h, changing lighter northwest by afternoon."