Some 3,000 residents of Sydney's Opal Tower, an apartment in the city's Olympic Park, are facing the possibility of spending Christmas in an emergency evacuation shelter after the building - and all buildings within a 1 kilometer "exclusion zone" - was evacuated following signs of "cracking" in the 33-storey building that have stoked fears about a possible collapse.

Emergency responders were called to the building Monday morning after residents on the tenth floor reported hearing loud "cracking" noises. An initial investigation determined that the building had moved one or two millimeters, according to the Guardian. Laser monitors are being used to scan for any additional movement in the building.

Though details about the evacuation are still trickling out, the Associated Press reported that police had to use heavy equipment to force open doors to allow residents to escape. Neighboring buildings have also been evacuated.

Opal

The tower has almost 400 one, two, three and four bedroom apartments, with two bedrooms selling for nearly $1 million. The tower is situated over the central site of the 2000 Sydney Olympics.

Fire officials in the city said it was "too soon" to tell on Monday whether the building was in danger of collapse. Acting Superintendent Greg Wright said his department couldn't offer a time estimate for how long the inspections would take. Water, gas and electricity service to the building has been shut off.

"We don’t know that until the engineers assess the building and have a look at what caused the issue and if there is a major issue with the building...It’s not going to be done in minutes. Hopefully it doesn’t take much longer than hours," he said.

Residents had been taken to the Royal Agricultural Society Hall, but many have now been rehoused. Meanwhile, trains will skip the Olympic Park stop that runs near the building. Buses will serve the area instead, according to Channel 9 News.

The engineering firm that helped build the tower released a statement after the evacuation describing a potential complication that may have contributed to the "cracking" sounds.

Wood & Grieve Engineers, who worked on the building, said online: "The large structural offsets at the base of the towers created a particular challenge. The difficulty was in the coordination of transferring sewer and storm water services through the deep transfer beams and large transfer slabs."

"Due to the height of the building which imposes excessive pressures on the pipework and fittings installed on the lower half of the building, the WGE team came up with a unique dual stage pressure control concept and conducted a series of experimental tests to simulate the real working condition of the system before specifying it for installation in the building."

Roads have been blocked around the building, including both sides of Australia Avenue. But one event that hasn't been canceled is a BBL cricket match between Sydney Thunder and the Sydney Sixers, which will be held at Spotless Stadium. Fans have been asked to travel to the stadium by bus and enter through a side entrance.