In fewer than three weeks, a crack has turned into a slip.

First it was a crack, now the whole back half of a North Shore carpark has slipped away.

The rear section of Rawene car park in Auckland's Birkenhead was closed off by Auckland Transport for safety reasons on September 20, following the subsidence of an already existing crack.

Fewer than three weeks later, the crack has become a slip.

LAINE MOGER/STUFF A subsidence in a Birkenhead car park has created even more headache for ongoing row between local business owners and Auckland Transport.

The manager of a nearby business, who did not want to be named, said the subsidence had got progressively worse.

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"Once a crack occurs and it starts raining all the water goes in there and makes it weak."

LAINE MOGER/STUFF A land subsidence in a Birkenhead car park has worsened dramatically in the past 12 days.

He said he couldn't see the problem being fixed any time soon.

Auckland Transport's Mark Hannan said investigations were still underway and staff were "actively monitoring the slip".

He said there was "no danger to the public" but was asking people to respect the cordon.

LAINE MOGER/STUFF It had also spread to a neighbouring hillside.

"We have an engineering geologist on site today to assess and provide recommendations," Hannan said.



"Engineers are working to determine the stability of the fill and whether we need to cordon off further areas of the car park."

Hannan had previously denied the cause of the crack was linked to adjacent construction work by private developers Chelsea Bay due to the fact the car park was built on an embankment of landfill.

However, nearby residents weren't convinced, saying the construction work was so loud it shook neighbouring building Rawene Chambers, and that the car park had been fine until construction took place.

LAINE MOGER/STUFF Part of the car park was closed because of the subsidence by September 25.

Mokoia Ridge resident David Corlett said he was concerned that Auckland Council has underestimated the impact of pile-driving on unstable land.

The Chelsea Bay developers and Auckland Transport had been contacted for more comment.

Kaipatiki Local Board deputy chairman John Gillon said he had also contacted AT.

SINKHOLE OPENS IN ROAD

Meanwhile, in south Auckland a huge hole has opened up in a rural road.

A section of Kingseat Rd had been closed on Monday afternoon, police said.

The affected area was between Glenbrook and Pearson roads near the village of Patumahoe.

"The road will be closed ... for the foreseeable future as engineers assess the hole, which is approximately 2m x 2m in size," police said.

"Motorists are asked to use the diversion in place via Pearson Rd."

The hole had formed due to recent rainfall, police said.

GNS Science said natural sinkholes generally form in terrain which is underlain by soluble rocks, such as limestones and chalks.

Water moving through the rocks slowly dissolves them, creating underground holes which are visible when the ground above them subsides.

Sinkholes can also appear when loose soil and silt is eroded by underground water.

They can also be caused by human error, such as incorrect design of a tunnel or mineshaft.

The cause of a sinkhole, such as a broken pipe or design flaw, needs to be addressed before the sinkhole can be repaired, GNS Science said.