A number of residents fled the building after hearing"cracking noises"throughout the morning,police said in a statement.
Fire and Rescue NSW and police attended the scene and after establishing the presence of a crack on Level 10 of the building,evacuated the remainder of the residents,setting up a 250-metre exclusion zone.
Police said engineers had informed them the building had moved 1-2 millimetres but it was unclear whether further movement had occurred or would potentially occur.
In addition to the exclusion zone,water and gas have been shut off and the tower was being isolated from the power grid as engineers were sent into the building to assess the structural integrity,Mr Wright said.