Some residents fled the building immediately. After police and Fire and Rescue NSW arrived at the scene to find a large crack on the 10th floor, up to 3000 people were evacuated from the building and its surrounds as a 250-metre exclusion zone was established. An evacuation centre was set up at the Royal Agricultural Society Centre. Loading Replay Replay video Play video Play video At 12.30am, police said most units had been declared safe and residents were able to return. However, 51 of the 392 units in the Opal Tower were declared structurally unsafe. Occupants were escorted in to gather their belongings and find alternative accommodation. NSW Police Acting Assistant Commissioner Julie Boon said "an internal support wall failed" in the building.

Fire and Rescue's Urban Search and Rescue team, made up of specialist engineers, entered the building at 7pm and worked through the night to assess each floor. “It’s been a particularly frustrating time for residents and we’re very aware they are keen to go home the night before Christmas," Ms Boon said shortly before the majority of units were given the all-clear. "This is a large building and it’s critical the safety of the residents comes first." Among those residents who ushered in Christmas Day on the concrete floor of the Sydney Showgrounds exibition hall were the Seniors, who came to Australia for a three-week holiday. “Even if it is safe we’re not going to be sleeping there,” Ms Senior told the Herald. “How can you sleep in there thinking the building might collapse? You wouldn’t be able to rest. I wouldn’t anyway. “We won’t be going anywhere unless we can get back in and get back out but I don’t know if we would be able to do that.”

The Seniors were staying on level eight, two floors below where the internal wall failed. The family were sightseeing on Sydney Harbour on Monday afternoon and came back to the horror news they would not be allowed back in amid “cracking noises” being heard within the complex. Roads were blocked off around the apartment on Monday afternoon. Credit:AAP Presents, passports, clothes, luggage and a hire car were all still in the apartment block, which they feared they may not get back into if the green light is not given. “I wouldn’t want to go in there and get the belongings if it wasn’t deemed safe,” said Leon Senior. “I wouldn’t even get the car.

“We spoke to people in the building and they got told to evacuate … they thought it was a fire.” Loading As she spoke to the Herald, a notification lit up Fiona’s phone. “A woman from Airbnb just got back to me saying she’s going to try and help find a solution to sort us out. She said she’s going to get back to us as soon as possible. We can only hope I suppose. What a way to spend Christmas.” On Christmas morning, another resident was packing up and leaving the building because he said he would not feel safe going to sleep. He gathered his bags, his cat and left with his mother, who said the situation had "put a real dampener on things". A resident leaves Opal Tower on Christmas morning. Credit:Nick Moir

Engineers and building managers remained on the scene on Tuesday morning and the cause of the cracking was not made clear by authorities. Nearby buildings were evacuated for about 12 hours, including the Botania building, operated by Meriton, which told residents in an email that as "there is a potential for the tower to collapse, a 1km radius has been evacuated". Botania resident Roman Teslyuk, 26, and his wife Christina, 27, said by about 8pm they had given up hope of returning home on Monday night and would be waking up on Christmas morning in a Potts Point hotel – along with the dog they managed to rescue from their apartment after initially being told only children would be brought to safety. Temporary home: Affected residents inside the Sydney Showgrounds' exhibition hall late on Monday evening. Credit:Tom Decent "The cops at the entrance said if it’s a child they would get it out but if it’s a dog they wouldn’t," Mr Teslyuk said. But he found an unguarded entrance and went into the building to retrieve his dog.

Police Detective Superintendent Philip Rogerson said on Monday evening the building had shifted between one and two millimetres as a result of the issue. But there had been no further movement detected on laser monitors deployed by emergency services. Police evacuated 55 children from a nearby childcare centre and released them to their families. There have been no reports of cracks at the building prior to Monday, authorities confirmed. The website for the Opal Tower says the building has 392 apartments, commercial spaces, a childcare centre and community centre. The development, which was completed in August at a cost of $165 million, includes a retail precinct and childcare centre for 80 children.