The team of firefighters had responded after midnight to an alert about a gas leak in the small town of Quargnento in the Piedmont region of the country, police said.

As the firefighters attempted to put out a fire in an abandoned farm building, the explosion occurred, bringing down the entire structure and killing the three men.

Firefighters working in the rubble of the ruined farm building following the explosion on Tuesday morning. Photo Italian firefighters/The Local

In a nearby building, authorities found an unexploded gas cylinder, a timer, and electrical wire, the local prosecutor said.

“All this leads us to believe that the explosion was intended and deliberately set,” local prosecutor Enrico Cieri said.

Part of the device believed to have caused the explosion. Photo: Italian firefighters/The Local

Two other firefighters and a member of Italy's Carabinieri law enforcement corps were injured in the incident.

Those killed were aged 32, 38 and 46, Italian firefighters told The Local.

The Local understands that emergency services workers on the scene believe the fire may have been set intentionally, and that the explosion was not an accident.

“There's something very wrong here,” said one source. “If this was done deliberately, I can't understand why. But that is what it looks like.”

Local press reports said investigators were looking into possible insurance fraud or a family dispute behind the inferno.

On social media, the Italian fire brigade paid tribute to those killed, saying the fire service felt “pain” at the loss of the three colleagues.

The Italian fire brigade also released an aerial video showing the area where the incident took place.