A man suffered life-threatening injuries from an assault on a busy Carlton street in Melbourne.

The 32-year-old was rendered unconscious after he was punched three times to the face before he fell and hit his head on the footpath.

The victim of the Carlton assault in hospital. Credit:Seven News, via Twitter

Senior Constable Adam West said police were told a man and a woman approached the 32-year-old and his 30-year-old male friend on the corner of Lygon Street and Elgin Street at 12.40am on Saturday.

He said the man punched the 32-year-old before he fell and hit his head. The attacker then approached the 30-year-old friend, but was stopped by his female companion and the pair left.