Rescue personnel in four-wheel drive vehicles are on call to ferry residents trapped on either side of a collapsed bridge in the suburb of Birchville, says Upper Hutt mayor Wayne Guppy
Sixty-two homes have been cut off since a torrent of water knocked out the middle pier on the bridge over the Akatarawa River this morning.
Mr Guppy said residents who needed to get in or out could call the council's welfare line to arrange for transport by four-wheel drive via a track from Totara Park.
"People have obviously got medication that they need to get, or they've gone off to work and their family is seperated, and of course there will be pets and things at home, so we've got people on the ground there working to make sure everyone can get home or get families and everyone together.
Mr Guppy said the river level was still too high to carry out a full assessment but it was expected the bridge would need to be completely replaced.
The council may bulldoze the track to create road access.
Upper Hutt City Council operations manager Lachlan Wallach said engineers had carried out a preliminary assessment and were now working with specialised bridge engineers and infrastructure service providers to determine the extent of the damage.
"The river is very high and very fast and it looks like the centre pier may have got undermined and it's dropped and twisted, which means it's dragged the bridge deck down with it. So the bridge deck is now about a metre below where it should be in the middle, so it is like it's broken it's back"
Tonight, council workers on quad bikes are doing a leaflet drop to residents.
Sewage was discharging into the river from pipes damanged by the collapse but this has now been restored.
Residents are discouraged from flushing their toilets due to lack of water supply.
About 140mm of rain was recorded at Taungata in the Tararua Ranges between 1pm Wednesday and midday today.
The collapse of the bridge at Bridge Road in the Upper Hutt suburb of Birchville has cut off 70 properties.
Naomi Hutchinson is one of the stranded residents where the bridge collapsed.
She said the bridge was crucial infrastructure for Birchville residents.
"I don't know what the plan is but from what I have heard, it looks like we need a new bridge. The other issue is that the bridge carried the water and the gas."
Another resident, named Brian, said he had been watching the bridge since midday and it appeared to be still slumping.
"I was horrified, I mean I go across there resonably regularly. It looks like the middle pilalrhas been washed out, and since I've been here it's got worse - it's starting to buckle now."
MetService said the heavy rain north of Wellington was now easing.
"There will still be some rain and showers affecting the Tararua Range until about 3am Friday morning, but it's not going to be as intensive."
On the Kapiti coast, the weather eased late this afternoon.
The Akatarawa Road, which was blocked by a mudslide earlier today, and the Ōtaki Gorge Road, that had been passable only by ute, have been fully reopened in the last half hour.
A spokesperson for the Kāpiti Coast District Council said some riverside reserves were still closed but water levels continue to recede and all crews had been stood down.
Earlier, Kāpiti Coast District Council civil defence controller Scott Dray said the council had received about 20 calls for help, six of which were requests for sandbags.
Staff had pumped out two private properties and one piece of reserve land.
"We are not aware of any private homes being flooded - just sections and possibly one garage at this stage," he said.