About 4pm a 56-year-old Lalor Park man was travelling east along Bells Line of Road, when he lost control and the motorbike fell onto its side.

The rider was treated at the scene before being airlifted to Westmead Hospital where he remains in a serious but stable condition.

Officers from Chifley Police District established a crime scene and are investigating the circumstances surrounding the crash.

Anyone with information about the crash is urged to come forward.