Poor work and bad weather caused part of a building site and a driveway to collapse into a northern Sydney construction pit, an engineer says.
Wet weather is hampering efforts to stabilise a three-storey Collaroy unit block just four metres from the pit.
"It's unfortunate that this continuing wet weather appears to have softened the ground around and they've had a collapse due to inadequate shoring," geotechnical engineer David Dickson told the Seven Network.
The 12 units were evacuated after emergency services were called early on Tuesday due to a gas main being ruptured in the collapse.
It's been fixed and gas has been restored to the units but the residents won't be able to return home for at least one night.
"The evacuations will remain in place until the area is deemed safe," police said.
Neighbour Wendy Hill, who lives in a heritage-listed house, said the development had been "scary".
"The development which is literally one metre from our house down nine metres has been causing us a lot of sleepless nights," she said.
Fire crews and engineers have been assessing the site all day and builders have been told to backfill under the collapsed driveway.
Most firefighters have left but police will remain at the scene.
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