The tradie who died when scaffolding collapsed at a building site in Sydney has been identified as an 18-year-old apprentice.

Christopher Cassaniti fell from the almost eight-storey structure and became trapped under the debris in Macquarie Park.

A 39-year-old co-worker remains in a critical condition at Royal North Shore hospital.

Christopher Cassaniti only celebrated his 18th birthday a few days ago. The apprentice died today after a scaffolding collapse at a Macquarie park construction site. (Facebook)

The two men were working on a 17-metre structure to the rear of the building when it collapsed at around 12.30pm.

The teenage victim’s distressed parents visited the scene of the accident at the Lachlan's Line apartment project on Epping Road.

When Mr Cassaniti turned 18 last week, his mother Patrizia sung the praises of her "compassionate and shy, yet strong and forever helpful" son.

"We wish you all the best that the world can dish out and May God be forever in your heart and bless you with much joy, happiness and most importantly health," she posted to Facebook.

His friends have posted tributes to Facebook.

"You were a fantastic bloke and had a heart of gold," Benjamin Betros said.

"You have been my friend since the first day of kindergarten .. words can't express how much this hurts," Bella Mineo said.

Due to the amount of debris in the collapse, it took rescuers some time to reach the trapped men.

“The first resources that arrived on scene found an absolutely chaotic and emotionally charged scene that took some time to ascertain what had happened,” NSW Ambulance spokesman Steve Vaughan told 9News.

"The injuries were significant."

Co-workers were devastated by the workplace accident, with a chaplain service being offered to those affected. (9news)

Two men were trapped at a construction site on Epping Road in Macquarie Park. (9News)

When paramedics finally reached Mr Cassaniti, almost two hours after the collapse, he was confirmed dead at the scene.

“I heard people in there screaming ‘help us, help us, help us’ and screaming obviously in pain with all the metal that had fallen on them," witness Albert Muscat told 9News.

"We started cutting with the grinders and hammers until about 20 minutes later we couldn’t hear screaming anymore, that’s when the supervisors told us to move out.”

As many as nine ambulance units, a Careflight helicopter and multiple Fire and Rescue NSW crews were deployed to the site to assist with the operation.

An eight-storey scaffolding structure collapsed at the construction site this afternoon, killing one and critically injuring another. (nine)

A man was taken to Royal North Shore Hospital in a critical condition after the scaffolding collapse in Macquarie Park this afternoon. (9news)

Authorities arrived just before 12.30pm and have remained on scene collecting evidence. (9News)

Several NSW Ambulance crews were required and there were traffic delays on Epping Road for eastbound traffic.. (9News)

Police had two eastbound lanes on Epping Road closed while they were at the scene, causing traffic delays in the area.

All lanes have since reopened.