Man, constable punched in Sydney's CBD

A man has been charged with assault after punching a man on the street and a police officer in Sydney's CBD.

A 51-year-old man was walking along Park Street with a friend about 4pm on Friday when a stranger punched him in the head without provocation before walking off.

The victim reported the matter to police officers, who found the man on Castlereagh Street, where he punched one of the male constables in the face.

The Darlinghurst man, 38, was arrested and charged with common assault and assaulting police. He was refused bail to appear before the Parramatta Bail Court on Saturday.

The 51-year-old man and the constable were treated for minor injuries.