Man critical after west Sydney fight

A man is in a critical condition in hospital and another is under arrest following a fight in Sydney's west.

Police say the two men, aged 24 and 36, are known to each other and had an argument while walking from a party in Parramatta on Saturday night.

In the ensuing fight the 36-year-old was pushed to the ground and hit his head on the footpath, causing him to lose consciousness.

Witnesses came to his aid and he was taken to Westmead Hospital where he remains in a critical condition.

A 24-year-old man is assisting police with their inquiries.