Unit owners in Sydney's evacuated Mascot Towers building have learnt the repair bill could blow out to $20 million as construction engineers zero in on what caused the complex to crack.

Key points: Unit owners voted to raise $7 million in special levies for remediation works to start

Unit owners voted to raise $7 million in special levies for remediation works to start Engineers have focused on construction and development work in the nearby area as a possible cause of the cracking

Engineers have focused on construction and development work in the nearby area as a possible cause of the cracking The ABC understands the NSW building commissioner conducted an on-site inspection at a construction site near the towers

At an extraordinary general meeting in Sydney on Thursday night, the owners of units in the beleaguered towers complex voted to raise $7 million in special levies for remediation works to start.

The meeting was also told the repair bill for the remediation works at the 132-unit block could run as high as $20 million, which is about $150,000 for each unit

They had earlier rejected a $10 million special levy loan, which would have incurred more than $3 million in interest, and will begin paying the first instalments in October.

Resident Brian Tucker said it was an exhausting night.

"There's a lot of people that are really financially stressed, people are just so distressed," he said.

Engineers, who have been assessing the damage at Mascot Towers and believe they know what caused the building to crack also spoke at the meeting, which ran for more than four hours.

However, they did not make their report public.

One of the cracks in Mascot Towers, in Sydney's inner-south. ( AAP: Bianca De Marchi )

Patrick McGuire, from the building's owners corporation, said the engineers had been focusing on the "construction and development work" in a nearby area.

"The engineers indicated that the building had to be stabilised ... they had in their view some fairly clear ideas about some root causes as to the building (cracking)," Mr McGuire.

"The only detail that I'm prepared to say is that it related back to construction work within the general precinct."

Residents were evacuated in June due to cracking in the primary support structure and have since been living in temporary accommodation.

Last week, NSW building commissioner David Chandler launched an attack on the builders of the troubled towers complex and described the development as one of the most poorly built constructions he had seen.

"I'm quite certain that the builder didn't know how to read any construction plans, because the faults that are in that building are simply someone who didn't pay any attention to them," he told a NSW Upper House inquiry.

The ABC understands Bayside Council officers had on Monday accompanied the Building Commissioner for an on-site inspection of the building next door to the towers, at 27 Church Street.

Mr Chandler said he had not seen many buildings as "poorly built" as Mascot Towers. ( AAP: Bianca De Marchi )

The developers of the adjacent building denied the construction at their site was in any way to blame and that the "existing damage" at Mascot Towers was unrelated to them.

Residents have been told there may be a staged return into the building and that some of them maybe able to move back into the apartment block early next year.

The Mascot Towers fiasco came after another apartment building — Opal Tower, at Sydney Olympic Park — had to be evacuated on Christmas Eve last year after cracks were discovered.

"We come to this country thinking of how much of a future we'll have compared to back home, but we end up like this," said a Mascot Towers resident who requested anonymity.

"It's not fair. Because of someone else's fault we will have to bear all the consequences."