A man was seen walking into the business on Wickham Street with a jerry can.
It is believed there was a scuffle with the staff inside, before footage showed their brawl spills out onto the street.
The owner of the store was assaulted and injured, and left the scene.
The alleged attacker then re-entered the shop, and moments later a fireball erupted, with flames flying onto the footpath.
Police said the arsonist may have burnt himself or his clothes may have been caught in the fire.
A man’s shoe was also found near the scene, according to police.
“Given the state of the shoe that was found, it’s possible that he might have some significant burns,” Inspector Jane Healy said.
Police believe this was a random attack but are investigating several leads, including whether the man had a getaway driver.
The fire burned for hours with a dozen fire crews called to the scene.
Nearby surrounding heritage buildings were saved from the blaze.
Police are still looking for the alleged arsonist.