Melbourne gym targeted by arsonists two days in a row

Fire crews were called to the gym in Montague Street. (ABC News)

A gym in South Melbourne has been targeted by arsonists twice in two days.

Fire crews were called to the Rare Breed gym in Montague Street just after 3am this morning.

A police investigation began after the gym was targeted the previous day.

A gym in South Melbourne has been targeted by arsonists for a second night in a row.

Fire crews were called to the Rare Breed gym in Montague Street about 3:13am this morning.

Fire Rescue Victoria (FRV) said firefighters arrived within seven minutes to find smoke and flames coming from the single-storey building.

"FRV crews donned breathing apparatus and used hose lines to conduct an external attack on the blaze," a spokesperson said.

Fire Rescue Victoria said the blaze was extinguished in about 40 minutes. (ABC News)

"The incident was declared under control at 3.59am, approximately 40 minutes after crews arrived on scene.

"The cause of the fire is deemed to be suspicious, and it will be investigated by Victoria Police."

It is the second time in consecutive days that the gym has been targeted by arsonists.

On Tuesday morning about 3:50am a white vehicle rammed the roller door of the gym and a fire was lit inside the premises.

A police investigation into the incident is ongoing. (ABC News)

The incidents are being investigated by Port Phillip Crime Investigation Unit detectives.

No arrests have been made and police said the investigation was ongoing.

Anyone with information has been urged to contact CrimeStoppers on 1800 333 000.