Up to 3000 residents have been evacuated from multiple buildings at Sydney Olympic Park amid loud "cracking noises" being heard within the recently-completed Opal Tower apartment building, sparking fears of a collapse.

An emergency operation launched on Monday afternoon remains in place, with an exclusion zone set up that includes the train station and neighbouring apartment buildings as engineers, firefighters and paramedics entered the building to assess its structural integrity.

"It’s not going to be done in minutes, hopefully it doesn’t take much longer than hours," said Fire and Rescue NSW spokesman Greg Wright as the assessment got under way on Monday evening.

Concerns were raised over the new 36-storey residential building on Brushbox Street, next to Australia Avenue, at about 2.45pm.