Two people were set on fire when an ejected nightclubber hurled a molotov cocktail at the Melbourne nightspot after assaulting two security guards.

A 34-year-old man man allegedly threw a plastic bottle filled with accelerant at a Thornbury nightclub, in High Street, about 2.30am (AEST) last night.

It hit a shop front window, causing minor damage, and set fire to the bottoms of two patrons' trousers.

A 40-year-old man suffered minor burns.

Police said the man had been thrown out of the club half an hour earlier and had assaulted two security guards and threatened to kill them before returning with the molotov cocktail.

A man was arrested at a Thornbury house later in the morning and was bailed to appear in Melbourne Magistrates' Court on Monday.

Detectives have spoken to patrons and are calling for other witnesses to come forward.