Police arson specialists and forensic officers arrived from Melbourne on Friday afternoon to investigate the cause and origin of the blaze.

Detective Senior Constable Matt Pascoe said it appeared a kitchen in the rear of the building endured the worst effects of the fire, but there was "significant damage" throughout the property.

"We've determined that the fire's been deliberately lit and are now commencing an investigation into the offence of arson," he said

A passer-by first reported the fire at Marciano's Cafe Plus, 4 Perrin Street, at 5am on Friday morning.

Emergency services were notified and the Country Fire Authority sent two tankers to extinguish the blaze.

Detective Sen Constable Pascoe said the shop was then under "crimescene guard" for most of the day until the specialists arrived.

"Our own enquiries revealed very little, other than it was still being treated as suspicious," he explained.

Detective Sen Constable Pascoe said there had been some grass fires in the area recently, but nothing near the Robinvale CBD.

"Anyone with any information or any witnesses to the event are encouraged to contact police," he said.

Marciano's Cafe Plus has been open in Robinvale for about 16 weeks.