Emergency services were called to the Opal Tower at Sydney Olympic Park on Monday after those living in the recently-completed building heard and saw cracking in a wall throughout the morning.

Residents of 51 units in the 38-storey building are still unable to return to their homes after the units were deemed unsafe, and it appears unlikely they'll be declared safe any time soon.

The developer Ecove on Wednesday released a statement defending the Opal Tower as a "high quality building".

It said the builder, Icon, had full liability on the design and construction.

"Ecove has delivered a project that is well above the industry standard," Ecove director Bassam Aflak said.

"The important fact is that there is absolutely no danger for the residents. We're confident this localised issue can be fixed. Most people are now back in their homes."

Mr Aflak reassured residents they were covered under warranty: "Ecove will help them through that process."

"We've all been stunned by what's happened, and we've been heartened by the way the community has rallied to support the residents, from the emergency service crews and the Salvation Army, to the local businesses, hotels and other people who have worked through Christmas to help us through this time," he said.

"We, like the residents, are anxious that the builder defines the problem and resolves it as soon as possible."

Residents of the 51 units that are considered unsafe were escorted back to their homes to gather essential belongings on Tuesday.

Fire & Rescue NSW Superintendent Adam Dewberry didn't know when the units would be declared safe .

"It's not as if it's going to be tomorrow or the next day because there needs to be an element of work done, now it's just how quickly that work can be done by the engineers to get in and get a really good thorough assessment," Supt Dewberry told AAP on Tuesday.

Australian Associated Press