Some residents of a recently completed Sydney high-rise apartment block were Tuesday spending their Christmas in makeshift camps, after they were evacuated by authorities when ‘cracking noises’ in the building were heard.

Hundreds of people in the 38-storey Opal Tower in the Sydney Olympic Park and other nearby buildings were told to leave their homes on Monday after reports of ‘cracking noises’.

Some two-thirds of the units were declared safe to return to Tuesday morning, but 51 others were declared ‘structurally unsafe’, New South Wales state police said.

‘Residents of these units have been escorted back to gather their belongings and have made their own arrangements for accommodation,’ police added in a statement.

‘Engineers and building managers remain on scene.’

No one was injured during the evacuation.

The building moved ‘one to two millimetres’ during the incident and authorities said they found a crack on the 10th floor.

But firefighters said they were confident of the building's integrity, apart from the affected units.

‘No, there is no risk that the building can collapse. It's just the local structure has been compromised,’ Superintendent Adam Dewberry of NSW Fire and Rescue told the Australian Broadcasting Corporation.

‘What will happen now is the strata manager will work with the local engineers to determine what needs to be done to actually make this building safe and let the full occupancy reoccur.’

Residents spoke of how their Christmas plans were thrown into turmoil, with some saying they had to sleep in their cars.

Others said they were fearful of living in the block despite their apartment being assessed as safe.

‘I'm going to be moving, that's for sure. I don't want to spend a second in there that I don't have to. I don't want to die. I wouldn't feel safe sleeping there,’ 20th floor resident Chris Abram told commercial broadcaster Channel Nine.

The 392-unit tower opened this year and is near the site of the 2000 Sydney Olympics.

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