Up to 200 people were unable to return home last night while emergency services worked to secure a crane that collapsed into an apartment complex at Wolli Creek in Sydney's south.

Three workers were injured when the crane fell, with the construction union condemning the incident as "not good enough".

Two damaged buildings have been evacuated as well as residents in surrounding buildings, emergency services say.

Trains on the Airport Line between Central and Turrella have been cancelled as a precaution and Sydney Trains yesterday warned over 50,000 people could have their travel plans disrupted today.

"There may not be rail services to both the international and domestic airports [on Monday] morning," CEO Howard Collins said.

Just after 9:30am emergency services were called to Brodie Spark Drive following reports a crane had fallen from one building and onto a second building.

The workers injured in the incident were responsible for the erection of the crane and all three are being treated at St George Hospital, one for a suspected broken leg.

Police said no-one was inside the crane when it collapsed.

No-one was inside the crane at the time of its collapse. ( ABC News: Jean Kennedy )

It is believed a mechanical or engineering fault caused the crane to collapse. ( Supplied: Daniela Giorgiutti )

Fire and Rescue Superintendent Josh Turner said the priority was making sure no-one on or around the site was at risk.

"At this stage we are going to keep approximately 20 firefighters on site who are working with a USAR [Urban Search and Rescue] team and they have electronic movement devices on all areas around the building, the crane and the scaffolding to log what movement is happening," he said.

High wind in the area is currently making the situation more risky and exclusion zones will stay in place until further discussions with engineers, Superintendent Turner said.

Building managers are now working out where to relocate the approximately 200 people who will not be able to return to their units.

'Could have seen many lives lost'

CFMEU NSW state secretary Brian Parker said early investigations indicate it was a mechanical or engineering fault with the crane that caused it to collapse.

"We are very, very concerned about this particular issue," he said.

"In this day and age, and all the expertise we have, it's not good enough.

"We have seen cranes catch fire, fall out of the sky, but not cranes that collapse onto buildings that have residents.

"Our fears are not just for the workers that work to erect these cranes, but also the public."

The CFMEU is calling for a stop on any further erection of cranes until investigations are complete.

"It could have been a major disaster here today and we could have seen many lives lost," Mr Parker said.

SafeWork New South Wales has been notified of the incident.

'I don't think I'll ever live in a tall building again'

Mary Broadley who lives in the unit block the crane struck said she thought the whole building was going to collapse when she felt it start to shake.

"It was so noisy, it was just unreal the noise," she said.

Her husband Bill Broadley said it "was like a bomb going off".

Mary and Bill Broadley, with daughter Ashleigh, had their bedroom significantly damaged by the crane. ( ABC News: Jean Kennedy )

"I went to take a look and the crane was right outside the bedroom window," Mrs Broadley said.

The ceiling and the walls of the bedroom have cracked and the windows have smashed, she said.

"I could have been in the bedroom, or the kids could have been in there," Mr Broadley said.

"It was so scary, I don't think I'll ever live in a tall building again," Mrs Broadley said.