Residents of a recently completed high-rise apartment block in Australia that made "cracking noises" on Christmas Eve have been moved out again as engineers work "around the clock" to fix the issue.

Police and emergency services evacuated some 300 people in the 38-storey Opal Tower in Sydney and other nearby buildings on Christmas Eve after reports of "cracking noises".

The building moved "one to two millimetres" during the incident and authorities said they found a crack on the tenth floor.

Some two-thirds of the units were declared safe to return to on Christmas Day, but 51 others were declared "structurally unsafe".

The issue threw the festive plans of affected residents into disarray, with some telling local media they had to sleep in their cars while waiting to return home.

Others said that even though their apartments were deemed to be safe, they were too afraid to live in them.

The construction firm Icon has defended the tower, describing it as "structurally sound".

"The temporary relocation is a precautionary measure to allow engineers to work around the clock to comprehensively investigate and remediate the site in the quickest time frame possible, without further disruption to residents," it added in a statement.

Icon said that residents would be provided with accommodation and compensation, and investigators from global engineering firm WSP and its majority owner Japanese construction company Kajima would lead the investigation.

It is understood that residents were told at a meeting today that it could be up to ten days before they would be allowed back in the tower.

The New South Wales state government is already conducting an investigation into the building's structural integrity.

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