Icon said in a statement:"The building is structurally sound and the temporary relocation is a precautionary measure to allow engineers to work around the clock to comprehensively investigate and remediate the site in the quickest time frame possible,without further disruption to residents."

The company will pay for affected residents to stay at nearby hotels.

"The damaged section of the building has now been reinforced as a precautionary measure while a team of engineers carries out the investigation,"the statement said.

"The thorough investigation is being led by engineering firm WSP,with assistance from senior engineers from Kajima Corporation,one of Japan's largest construction companies and majority owner of Icon."

WSP Australia and New Zealand chief executive Guy Templeton said the collapsed concrete wall was"a failure"but"the overall integrity of the building is sound".

"Our view is that it’s best to have the residents move out of the building for a period and make sure that everything can be thoroughly and completely checked.”

A spokesman for Planning Minister Anthony Roberts acknowledged the evacuation was"incredibly disappointing"for those who lived in the tower,but said the minister had urged the developer to ensure residents'safety.

The 392-apartment block opened in August. The number of apartments that are currently occupied is unknown,as some units are empty or rented out on short-term letting site Airbnb.

Speculation and recriminations have flowed over the cause of the damage,with some experts pointing to a broader pattern of cost-cutting within the building industry amid the city's development boom.

Mr Roberts said two leading structural engineering experts would urgently probe the circumstances surrounding the damage.

Mr Roberts and Planning Department secretary Carolyn McNally on Thursday appointed Professor Mark Hoffman,dean of engineering at the University of NSW,and Professor John Carter,dean of engineering at the University of Newcastle,as specialist investigators to lead the government's investigation.

The findings will be made public.

Opposition planning spokeswoman Tania Mihailuk said the investigation should take in any recent work by the tower's developer and builder to ensure such a"catastrophic error"was not repeated.

"The NSW government needs to understand that there are potential ramifications across the entire sector for all new high rise developments and public confidence will need to be repaired promptly."

The project's developer,Ecove,hasdefended the "high-quality building". Ecove director Bassam Aflak said in a statement that Icon had"full liability on the design and construction of Opal Tower".

Mr Aflak hit back at suggestionsthe damaged tower pointed to a broader pattern in the building industry and said there had been"no cutting of corners".

"It’s too early to leap to any conclusions,for instance,to speculate on wider building issues because of what appears to be one failed panel."