Residents of a high-rise in Mascot, in Sydney's inner-south, have been evacuated as a precaution after cracks were discovered in the building.

Key points: Ninety-five apartments in the high-rise block have been told to evacuate

Ninety-five apartments in the high-rise block have been told to evacuate An engineer expressed concerns after inspecting the 10-storey building

An engineer expressed concerns after inspecting the 10-storey building He found cracking in the transfer slab beam supporting the building's primary corner

Fire and Rescue NSW was called to the Mascot Towers on Bourke Street about 6:00pm last night, after residents saw cracks forming in the 10-storey building.

Engineers assessed the building and began formally evacuating residents — including young children and pets — of the 131-unit block.

Superintendent Adam Dewberry said there were concerns about movement in the building, with residents evacuated "as a precaution … for general safety at this stage to ensure that there are no injuries".

"At this stage there is no thought that the building is going to have a catastrophic failure or collapse," he said.

Residents of 95 apartments were told to leave, while 35 apartments were unaffected. ( ABC News: Selby Stewart )

The building was built over a decade ago and consists of two towers on a single footprint.

Ninety-five units are affected, while residents of the remaining units have been told they can stay in the building.

Pets also had to be relocated. ( ABC News: Selby Stewart )

A temporary shelter was established at Mascot Town Hall for those unable to find alternative accommodation, but it appeared to be empty last night.

In a letter from building management, residents were told an engineer inspected cracking that had developed in the "transfer slab beams supporting the primary building corner".

"Following the inspection, the engineer raised concerns over the safety for residents in the building," the letter read.

"It has been determined that there will be a partial evacuation of the building, pending further monitoring of the transfer beams over the course of the next week.

"This will determine if the building is safe for reoccupation."

Opposition spokesperson for Innovation and Better Regulation, Yasmin Catley, said the problems at Mascot Towers were symptomatic of the Government having watered down building regulations.

"None of this cutting red tape here and cutting red tape there to save a few bucks … because at the end of the day buildings are being driven by price rather than quality and that is not good enough."

'It's had so many issues'

Mascot Towers houses 131 apartments. ( ABC News: Selby Stewart )

John, who did not wish to provide his surname, arrived at Mascot Towers to pick up his girlfriend, who was told to evacuate.

"[She] got a message from one of her flatmates at 7:00pm, basically saying … everyone has to evacuate tonight.

"She got the letter at seven o'clock and had to be out of the building at nine o'clock — just get all of her stuff and leave."

Unit owner Anthony says the building has had "issues from day one". ( ABC News: Selby Stewart )

Anthony, who did not wish to give his surname, owns one of the apartments and has lived in the building for 11 years.

He said tenants, including babies, were being denied entry to the building.

"We hope that the builders or the people who are responsible for this will be held accountable because it's had so many issues from day one.

"I guess defects happen in most apartments but you wouldn't ever have thought it would come to this.

"Especially after seeing the fiasco with the Opal Tower in Homebush, you would have never thought something like this would happen in metro Sydney.

"I hope the owners do all get together collectively to hold the right people accountable for this."