Police investigating a fatal crash involving a truck in Sydney's south-west say other trucks belonging to the company have been found to have defects.

A taskforce has been established after the incident near Campbelltown yesterday afternoon, in which one man travelling in a truck died and 14 other people were injured.

Inspector Phillip Brooks from the Traffic and Highway Patrol Command says police are now investigating the entire fleet of the company that owned the truck.

He says it will take time to assess whether the truck involved in the crash was defective, but the initial results from the fleet are a concern.

"That truck involved is extensively damaged and is subject of a technical examination by both the Metropolitan Crash Investigation Unit, the police scientific branch and also the Roads and Maritime Service," he said.

"However, the company is being directed to supply their trucks. Out of their fleet so far, six have been inspected. Five of those trucks have been identified with a range of defects."