Buller's Mayor says while things in the region are "looking a lot better" on Sunday, much still needs to be done before residents can return to their homes.
A State of Emergency was declared in the Buller District on Friday, with thousands of people evacuated from their homes as heavy rain caused severe flooding in the West Coast region.
Mayor Jamie Cleine told Newshub weather conditions and river levels had continued to improve overnight, but the clean-up will be a big job.
"Certainly the Buller River is now running at least a metre lower than what we were experiencing yesterday, so things are looking a lot better there," he said.
"We did have to issue a shelter-in-place order for people that were becoming flood-affected that we we unable to evacuate, simply because we did not have the resource or the access to be able to do that - so there will be a number of people who will have been in houses overnight that are potentially flood-damaged or have water issues."
He said over 2000 people were evacuated by the end of Saturday, with around half of those staying in welfare centres.
The shelter-in-place order would remain in place until around mid-morning, he said.
"There's a lot of surface water [and] flooding water around town and there will be hundreds of homes that have been flood-damaged I expect, so we're just going to need a bit of time and daylight to assess what parts of town people could return to much quicker, and what will need building assessments and things done."
The West Coast District Health Board said a medical centre was evacuated overnight as floodwaters continued to rise in the region. Eleven patients, staff and supplies were relocated to Club Buller in Queen St.
Residents in the area are being cautioned to treat all floodwater as contaminated.
"Sewage may be mixed with flood waters and can cause serious illness. That means you need to wash your hands thoroughly or use hand gel after coming into contact with flood water," the Health Board warned.
The Orowaiti Bridge reopened on Sunday morning, with traffic being managed by road controllers. Motorists are urged to take it slowly.
The State Highway 67 Buller Bridge and State Highway 6 along Coast Rd also reopened last night, but Buller Emergency Management said people should only travel if it's for essential reasons.
Cleine said the reopening of supply lines to the region made a significant difference.
"Everything is looking more positive than it was yesterday - it's just going to be working on getting people back to their houses," he said.
Meanwhile in Marlborough, the entire townships of Spring Creek and Tuamarina were evacuated after a State of Emergency was declared on Saturday.
Deputy Mayor Nadine Taylor said 900 people were evacuated from more than 500 properties across the region.
"Our stop-bank network held up very well considering this is our largest ever recorded flood - a far bigger event than the previous biggest in 1983."
She said the council would begin planning the recovery and repairs to the network and flood protection system on Sunday.
"But most importantly, we'll be helping our community as much as possible, especially ensuring people can get back into their homes."
Wellington was also hit hard by the wild weather, with motorists on Sunday being warned to take care on the roads.
Waka Kotahi NZ Transport Agency said crews were continuing to clear debris following the heavy rain and flooding on Saturday.
"State Highway 2 is now open, but under a 50km/h speed restriction due to remaining surface flooding and debris," Waka Kotahi said in a statement.
"Other parts of the lower North Island also experienced heavy rain and flooding yesterday, so there may be other areas where surface flooding and debris remain on the road.
"Motorists are urged to take extra care, drive to the conditions and expect delays while crews continue working to restore the state highway network."