The Opal Tower in Sydney. Image Credit: Twitter

Sydney: More cracks have been found in a recently completed Sydney high-rise apartment block that was evacuated on Christmas Eve, engineers said Tuesday, as residents remained locked out of the building.

Police and emergency services ordered some 300 people out of the 38-storey Opal Tower in the Sydney Olympic Park and other nearby buildings on December 24 after reports of "cracking noises".

Some two-thirds of the units were declared safe to return to on Christmas Day, but 51 others were declared "structurally unsafe". Authorities said they found a crack on the 10th floor.

Tower builder Icon on Thursday called on all residents to leave the building again to allow global engineering firm WSP and its majority owner, Japanese construction company Kajima, to "comprehensively investigate and remediate the site".

WSP chief executive for Australia and New Zealand, Guy Templeton, said engineers have now found two areas on level four that "show evidence of some, but lesser damage" compared to level 10.

"As a precautionary measure, propping is being installed to support level four and this will be completed by Icon Co by the end of today," Templeton added in a statement.

"The building is structurally sound overall."

The New South Wales state government is 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.