Structural engineers will try to stabilise a unit block on Sydney's northern beaches after heavy rain caused a landslip at a neighbouring building site.

Residents from the 12-unit three-storey block on Frazer Street, Collaroy, have spent the night in temporary accommodation after the land gave way on Tuesday morning and police say they’ll stay there until the area is deemed safe.

Police and firefighters are still on scene.

Some residents have been concerned about the construction site for some time.

“We just knew something like this would happen – you can’t dig out half the peninsula and expect everything else to stay in place,” one resident told ABC radio on Wednesday.

Structural engineers are still assessing the site and a laser system is monitoring the movement of a wall at the building site

When the rain eases trucks full of soil will try and fill the hole.

“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.

Neighbour Wendy Hill, who lives in a heritage-listed house, said the development had been “scary”.