Nelson-Tasman Civil Defence is urging residents to avoid all non-essential travel, even as the worst of the recent heavy rain appears to have passed.
Slips, surface flooding and significant damage have rendered many roads across the upper South Island unsafe.
Contractors are working urgently to clear critical routes and restore access to cut-off communities but say public interference is delaying efforts.
“Roads are unsafe for general travel due to flooding, slips, and damage,” Nelson Tasman Civil Defence said.
“If the road is closed, please do not use it – it is closed for a reason, and that is predominantly for your safety and the safety of contractors.”
SH6 remains closed between Murchison and Nelson, with Civil Defence advising any essential travel is to be diverted through Kaikōura.
Local roads are similarly affected, with live updates available on council and NZ Transport Agency Waka Kotahi websites.
Authorities are particularly concerned that premature travel is hindering emergency crews, who are prioritising access to communities still without power, drinking water or communication lines.
Helicopters have been deployed to conduct welfare checks in isolated areas such as Tapawera, Tadmor and Mārahau.
The water supply has been partially restored in Tapawera and Kaiteriteri, but boil water notices remain in place for some areas.
Civil Defence says water remains unavailable for certain properties along Kahu Close, Kimi Ora and parts of Martin Farm Rd.
Alternative water supply stations remain in place.
Caution is also urged around all water sources.
Residents using private bores are advised to boil water as a precaution, and contact with floodwater should be avoided because of possible contamination.
In Auckland, where surface flooding has also occurred, multiple agencies were called to a slip in Muriwai today.
A section of Motutara Rd dropped away, taking a power pole with it. Three houses were evacuated – one directly affected by the slip and two others as a precaution.
Fire and Emergency New Zealand assistant commander for Waitematā, Chris Lind, said: “The structure is intact, the debris is resting against the back of it. So you have a quantity of mud and soil and some trees, and obviously the water that has come through behind it.”
He said council geotechnical engineers and Fire and Emergency engineers had confirmed two of the properties could be reoccupied “when they need to be”.
Severe Weather Update! ⚠️
— MetService (@MetService) July 12, 2025
⛈️🌧️Heavy rain continues for the western high grounds through to early Monday morning, with the risk of thunderstorms & hail still lingering in some areas today.
❄️ Road snow warnings are in place for Lindis Pass and Crown Range Road tomorrow, take… pic.twitter.com/yF9VF1MDpa
The third property, immediately beneath the slip, is still being assessed.
Vector has isolated power to the area and contractors are working with emergency services to secure the scene.
Council geotechnical experts have also been dispatched to Victory Rd in Laingholm and Motutara Rd in Muriwai.
Auckland Council’s general manager of engineering, Paul Klinac, said one slip in Muriwai is now contained and affecting a single property, with no wider risk to neighbours.
The road has since reopened.
“The council and the Recovery Office are in contact with the residents to provide any support required,” Klinac said.
“The council will continue to provide support, including checking the safety of the building, as is needed.”
In the meantime, the public is urged to avoid affected areas and allow engineers and emergency services to carry out their work safely.
Nelson Tasman Civil Defence also reminded residents to be cautious regarding other post-flood hazards, including potential electrical faults, unsafe structures and contaminated floodwaters.
People are advised to stay up to date through official channels including local council websites, Civil Defence social media and local radio.
“Let’s look after each other. Check in with your neighbours. That can also be a great way to get important info.”