Emergency services are helping residents evacuate the 36-storey apartment building, Opal Tower, in Sydney Olympic Park amid fears the structure could collapse and after the building moved "one to two millimetres".
Residents called emergency services on Monday afternoon following reports residents heard "cracking" sounds throughout the morning, NSW Police said.
A limited number of 45 people who had been evacuated would be rehoused on Monday night, police added. The residents have been moved to the Royal Agricultural Society of NSW centre at Showground Road in the Park.
Residents from nearby properties have also been told to leave or are not being allowed back to their homes.
There were no injuries and the building has been secured.
"I have been told by the engineers the buildings have moved by 1 to 2 millimetres," Superintendent Philip Rogerson said at press conference held at the park on Monday evening.
But he cautioned however that engineers and firefighters would still need to make further investigations before making conclusions although residents had also commented there had been some movements in the building on top of "cracking sounds" on Monday morning. Fire and Rescue NSW and engineers have entered the building to assess its "structural integrity".
The building's property manager was also on site.
Both the police and Fire and Rescue said the building had no history of structural problems prior to Monday.
The 392-unit tower at 1 Brushbox Street was jointly developed by Sydney developer Ecove and the Sydney Olympic Park Authority (SOPA) and completed in August.
"We are aware of the concerns that have arisen with the Opal Building and confirm that the builder has been notified," Ecove chief executive Bassam Aflak told the Australian Financial Review.
"As a precaution the building has been temporarily evacuated whilst it is being assessed by the relevant authorities. We will provide updates once further information is provided by the authorities."
There is now a 250 metre exclusion zone around the building, water and gas have been shut off and the tower is being isolated from the power grid, Fire and Rescue Acting Inspector Greg Wright said.
Trains have been stopped as a result of the operation, the Transport Management Centre said.
Australia Avenue has also been closed in both directions and there are "significant local traffic impacts". The building sits at the intersection of Australia Avenue and Bennelong Parkway.
Earlier on Monday, Meriton, the developer and operator of the nearby Botania building told residents in an email that as "there is a potential for the tower to collapse, a 1km radius has been evacuated".
In 2015 during the development approval of Opal Tower, Meriton opposed the extension of the Opal Tower by two further floors.
"The proposed development is far in excess of the 20-30 storey provision in the SOPA Masterplan 2030. The proposed variation to GFA is not adequately supported by the generic statement provided," Meriton said in a submission.
The variation was considered reasonable and did not "result in an overall increase in building bulk", planning documents showed.
"The height, bulk and scale of the proposed development is appropriate and would not result in any unreasonable visual or amenity impacts to adjoining residential properties," documents said.
The changes led to the reduction of typical floor to floor heights from 3.2 to 3.1 metres.
The property also has a childcare centre, shops on the ground floor, and basement parking.
Opal Tower is at the southern end of the Olympic Park Parkview Precinct, part of the Sydney Olympic Park Master Plan 2030 to turn the park into a new town centre with new homes and amenities.
It is one of four towers that Ecove has built in the precinct, including the two-tower Australia Towers and 1 Australia Avenue.
The developer is currently developing a fifth tower, the 38-storey Boomerang Tower.
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