Road workers inspect the damage of a wash out on Bird's Hill, Nelson.

Bob Gordon at his home in Tahunanui, Nelson. Mud has pushed through his backdoor.

The rainstorm that hit Nelson-Tasman last week is the most intense to have ever been recorded in any urban New Zealand town.

The region is still reeling from the downpour, which saw peak falls recorded at 764mm over 48 hours in Golden Bay.

''This is not just exceptional - this has never happened before,'' said Nelson-Tasman Civil Defence operations controller Jim Frater.

Teams of geotechnical engineers, building inspectors and welfare officers were today re-inspecting the more than 100 homes across the region that have been red-stickered.

Geotechnical leader for the Civil Defence response Grant Maxwell said the aim was to have all affected homes either confirmed as being too dangerous to inhabit, or their risk downgraded to allow limited access, by Christmas.

The declared state of civil emergency, which will expire at midnight tomorrow, will be re-instated but only over Nelson and Golden Bay.

Owners of properties that remained too dangerous to enter would be allowed a brief window of access this week so they could secure some personal possessions, he said.

Geotechnical engineers replaced red with yellow stickers on 15 properties today as part of the process.

''So that's positive news for 15 families,'' he said.

Nelson City engineers have been assessing the risk to the pipe carrying the city's water supply, which was in danger of slip damage.

Nelson-Tasman Civil Defence operations controller Alec Louverdis said a slip below the pipeline on steep ground was threatening some 20m of the pipe.

Engineers hoped to start building a supporting fence below the pipeline tomorrow.

The cost of the damage to the region's homes and infrastructure was already being estimated to be in the tens of millions of dollars.

Mr Frater said Civil Defence managers briefed the region's MPs and Civil Defence Minister Chris Tremain this morning.

''We gave them an appreciation of what we were facing and the need for on-going support.''

Tasman mayor Richard Kempthorne said the huge bill would be split between the councils, the New Zealand Transport Agency, Civil Defence and the Government.

''It's do-able,'' he said when asked if Tasman could afford the bill. ''We have to.''

Rocks Rd will be closed indefinitely while the danger of continued slips was assessed. Mr Maxwell said engineers abseiled the cliffs today to better understand the risk.

But understanding if the land under threatened homes on the Tahunanui Bluffs would ever be suitable for future development would take a lot more time and research, he said.

Meanwhile Mr Kempthorne said holidaymakers with bookings at Pohara Top Ten Holiday Park could be safe in the knowledge that the camp would be open for summer.

Totoranui Camp was also open but only accessible by boat.

However the region's beaches remained closed because of sewage spills from the flooding.