An explosion probably caused by a gas leak killed five people in a town in northwestern Italy early this morning, flattening a two-storey building and damaging several others, firefighters said.

Five bodies were recovered from the rubble of the residential building in Arnasco, a small town in the Liguria region, and a woman was taken to hospital in a serious condition, fire service spokesman Luca Cari said.

"It was a large blast because it brought down an entire two-storey building," Cari said. "We haven't yet completed the investigation into the cause of the explosion, but it's compatible with a gas leak, and that's the only hypothesis we have at this point."

All of the building's residents were accounted for but firefighters continued to dig through the debris in case any of them had visitors. Inspections were also being carried out at nearby buildings damaged by the blast, Cari said.