Ent Centre roof collapse in Sydney

A worker is lucky to be alive after the roof of the Sydney Entertainment Centre collapsed on top of him.

The man was underneath the structure as it came crashing down during demolition works on Saturday morning.

The construction union says the worker survived thanks only to being shielded by the excavation machinery he was operating at the time.

CFMEU NSW Secretary Brian Parker claimed worker safety on the project was coming a distant second to deadlines and profits.

Mr Parker said if the roof had come down on a weekday, up to 65 workers could have been working underneath.

"It's only a matter of time until we lose another construction worker in yet another avoidable workplace incident like this," he said.

SafeWork NSW has launched an investigation into the incident.