Emergency authorities have moved to reassure residents of Sydney's Opal Tower that the building is at no risk of collapse, after thousands of people were evacuated on Christmas Eve.
While most residents have returned, 51 apartments - about a third - have been deemed unsafe and those living there are spending Christmas elsewhere as they await the all clear.
About 3000 people were initially evacuated from the newly constructed 38-storey building and surrounding areas after the alarm was raised just before 3:00pm on Christmas Eve.
Residents reported cracking noises and doors became jammed when the building moved "1 millimetre to 2 millimetres", police confirmed.
But NSW fire and rescue superintendent, Adam Dewberry, said he was very confident about the building's safety outside the affected units.
"No, there is no risk that the building can collapse. It's just the local structure has been compromised," he said.
"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."
A large crack was found on the 10th floor of the building, with emergency services and engineers monitoring the situation overnight after initial fears of a building collapse.
Police have said the cause of the crack and structural concerns was due to an internal support wall failing.
An "exclusion zone" has been established on one section of the building from the ground level to level 38, which emergency services are describing as "the impact zone".
About 12:30am on Christmas morning, residents of those units declared safe were allowed to return home.
NSW Police said residents of the units deemed to be structurally unsafe had been "escorted back to gather their belongings and have made their own arrangements for accommodation".
Susan Maguire and her son Joshua were among those evacuated. It is still unclear when they will be able to return.
"[I'm] shocked and scared because my favourite teddy is up there as well," Joshua said.
Lisa Bridgett had to relocate with her two young children, and said it was not the Christmas she had envisaged.
"It's just my kids are at that age where it's really exciting and the little things you do on Christmas Eve like putting the cookies out for Santa … and all that sort of stuff they're going to miss out on," she said.
"I'm really sad for them that they're going to miss out this year."
Six-year-old resident Gordon Zhang said "it's been a disaster Christmas".
He and his parents got home last night from shopping and were not allowed back into their apartment.
They stayed at the nearby Pullman Hotel overnight and have just arrived at the Opal Tower building to see if they can get in.
They will hope to be with their extended family for Christmas.
Some residents were frustrated by having to wait for information about exactly what was wrong.
One resident said he was not sure about going home.
"They said it's safe there but we don't feel safe. I just came from work and they blocked a road and they said you cannot go inside because of the structural issue," he said.
Engineers and building managers remain on scene.
There were no reported injuries during the operation.