Man in critical condition after Darlinghurst attack

A man is in hospital in a critical condition after he was allegedly attacked on a street in inner Sydney on Thursday.

The 55-year-old was standing on Crown Street in Darlinghurst at 10.15am when he was allegedly approached by a younger man.

Police believe the man, 34, was known to him.

The younger man punched and kicked the 55-year-old for a unknown reason until the older man lost consciousness and fell to the ground, police said.

It is thought his head hit the pavement.

The man was found lying on the ground a few minutes later by a passerby, who called an ambulance believing he had been hit by a car.

He was treated at the scene for multiple fractures to his skull and taken to St Vincent's Hospital in a critical condition.

Police arrested the 34-year-old man on Nickson Street in Surry Hills at 2.30pm.

He was taken to Kings Cross police station where he was said to be assisting officers with their inquiries.

Charges are expected to be laid.