Man dies trying to cross major NSW freeway

A man has died after being hit by two cars while trying to cross a major highway in Sydney, causing several other vehicles to crash.

He was walking south across three lanes of the M4 at Parramatta on Saturday evening when he was hit and about seven other cars then slammed into the back of the two vehicles that struck the man, a police spokeswoman told AAP.

The man died at the scene, on M4 eastbound near the Church Street exit in western Sydney.

A crime scene has been established and forensic officers will investigate.

Police aren't sure why the man was trying to cross the elevated highway, which has no footpaths.

The drivers of the cars which hit the man have been taken to hospital for mandatory drug and alcohol testing.