Two men have died after a horror three-car crash in Sydney's west overnight.

Richmond Road at Marsden Park was finally reopened this morning nine hours after the fatal crash.

Police say a Subaru rear-ended a Mitsubishi travelling in the same direction on Richmond Road about 9:20pm.

The force of the initial crash pushed the Subaru into the path of an oncoming Hyundai travelling on the opposite side of the road.

The Subaru came to rest on its roof after rolling along the road.

The 29-year-old driver of the Subaru died at the scene.

The 22-year-old Hyundai driver died early this morning after suffering critical injuries following the head-on crash. He was flown to Westmead Hospital for treatment but could not be revived.

The 22-year-old female driver of the Mitsubishi was not injured in the crash.

Police are now investigating the cause of the crash and anyone who witnessed the crash or has dashcam vision of the accident is being urged to come forward.