A teenage motorcyclist has been killed in a collision with a four-wheel-drive in Sydney's north-west, police say.

The crash occurred at the intersection of The Driftway and Londonderry Road at Londonderry, near Richmond, about 11.20am on Thursday.

A NSW Ambulance spokeswoman said the motorcyclist died at the scene. Police later identified him as a 19-year-old man.

Paramedics treated two other patients from the four-wheel-drive for what are believed to be minor injuries.

Initial reports to emergency services suggested that an army truck was involved in the crash.

However, the truck is believed to have stopped at the crash scene to try to help the victim.

Police from the Penrith Local Area Command have launched an investigation and have appealed for any witnesses to contact Crime Stoppers on 1800 333 00 or to use the Crime Stoppers online reporting page.