An investigation is underway after a suspected arson attack on an acai cafe in Melbourne spread to adjoining businesses.

The Acai shop on Mahoneys Road in Campbellfield was completely alight by the time police arrived at 3.40am.

No one was inside at the time, Victoria Police said. 

Fire and Rescue Victoria arrived four minutes after triple zero was called, but the fire had already consumed the 10 by 30 metre single-storey store.

It’s understood two people were seen behind the shop, setting it alight before fleeing.

The blaze then spread to adjoining businesses, including a pet shop.

Unfortunately, hundreds of birds, fish and rabbits were killed in the fire.

Twenty baby turtles and some Mexican walking fish survived the blaze.

The owners of the pet shop told 9News they were devastated.

The owner of the acai shop moved to Australia four years ago, opening the shop five months ago.

He told 9News that he doesn’t have any enemies and doesn’t know why he was targeted. He said he is uninsured.

Victoria Police and VFR say the blaze is being treated as suspicious. An investigation is underway.

The suspected arson marks the fourth acai shop to be firebombed in Melbourne since February.