Man struck by car in Sydney altercation

A man is in a critical condition after he was hit by a car as he lay on the road following a fight in Sydney's west.

The 21-year-old man was with friends when they became involved in some sort of altercation, after which he ended up lying on the road outside a service station in Blacktown.

He was struck by a car driven by a 65-year-old man.

The man was taken to Westmead Hospital in a critical condition.

A 25-year-old man is currently in police custody as a result of the incident.