Man dies after jumping into Sydney traffic

A post mortem is expected to confirm whether or not a man who died after jumping into moving traffic in Sydney's west was under the influence of drugs.

Police say the 29-year-old man was hit by the wing-mirror of a small, slow-moving car on the Great Western Highway at Parramatta on Tuesday night.

Witnesses said he appeared to jump.

After being struck by the car - which drove on - he collapsed and was found crawling on his hands and knees on the road.

He later died in hospital and police believe he may have been affected by drugs.

They're appealing for the driver of the car that hit him to come forward.