Suspicious fire destroys Vic gym

A small but intense suspicious fire has gutted two factories used as a gym in Melbourne's southeastern suburbs.

Fire investigators are scouring a Melbourne gym for clues after a suspicious fire.

Emergency crews were called to the Berwick gym at 8.30pm on Tuesday to find an intense fire had gutted two small factories.

CFA spokesman Andrew Turner said foam mattresses inside the gym caused a lot of heat and thick black smoke.

"It was an intense, confined space fire," he said on Wednesday.

The fire caused minor damage to adjoining buildings and is being treated as suspicious.