Just days after turning 18 years old, a New South Wales man working at a construction site in Sydney's northwest died after a scaffolding collapse.

Christopher Cassaniti - a formwork apprentice - and another 39-year old worker were trapped under steel and concrete that fell from 15 meters.  Mr. Cassaniti died at the scene, and the other man remains in hospital in a critical condition.  Cassaniti's mother also worked at the site operating a coffee canteen.  She and the father were at the scene of the disaster in just minutes.

"The mother and father were here and took it very hard as you would imagine," said Construction, Forestry, Maritime, Mining, and Energy Union (CFMEU) NSW state secretary Darren Greenfield.  "To lose their 18-year-old son, new to this industry, early in his working life, and to lose his life doing a job, it's atrocious."

NSW Police from the Ryde Area Command and SafeWork NSW will investigate the incident.

"While the cause of the collapse is unknown at this stage, SafeWork is employing significant resources to fully understand how this tragic incident occurred," a spokeswoman said.  "It is expected that the investigation could take some time, while SafeWork inspectors work through the complexities of the incident."

Chinese-backed residential developer Greenland Australia is developing 900 apartments in six towers at the Epping Road site, with construction company Ganellen handling the building.  Synergy Scaffolding Services was responsible for the scaffolding.