One worker has been rescued and at least one other remains trapped after scaffolding collapsed at a construction site in Sydney's north.

A major rescue operation was sparked after emergency services were called to the scene on Epping Road, Macquarie Park, about 12.20pm.

A Fire and Rescue NSW spokesman said seven fire crews, including a crew that specialises in structural collapses, were at the scene, after receiving calls that two workers were trapped under a large amount of fallen scaffolding and concrete.

The spokesman said one person had been removed from the rubble. That worker has been taken to Royal North Shore Hospital in a critical condition, an ambulance spokeswoman said.

Three ambulance crews and the CareFlight helicopter were at the scene and police were also assisting with the rescue.

Two eastbound lanes of Epping Road are closed, and members of the public are being urged to avoid the area.

More to come