Arson expert to comb Melb restaurant fire

An arson expert is set to examine the scene of a Melbourne pizza restaurant fire.

The blaze, which started in the rear of Delizio's restaurant on Lygon Street in Carlton after 4am, is being treated as suspicious, authorities say.

Firefighters had to gain access through the restaurant's windows and were able to contain the fire to the kitchen area within 25 minutes.

Thick smoke enveloped the restaurant.

MFB commander George Arnold says the damage bill is substantial.

"I couldn't put a cash figure on it, it's quite substantial," Mr Arnold told 3AW on Wednesday.

Police say an arson chemist will examine the scene on Wednesday morning. A crime scene guard remained at the site overnight.

Police will continue their investigations on Wednesday.