ROME — A two-story building collapsed in the southern Italian province of Naples early Sunday, killing two young siblings and burying their mother and another woman in the rubble, firefighters said.

The firefighters said on their official Telegram channel that a gas explosion likely caused the collapse.

Rescuers in the town of Saviano recovered the bodies of a 6-year-old boy and a 4-year-old girl. Their 2-year-old brother was found alive and the father was hospitalized in Naples in serious condition.

Firefighters’ spokesman Luca Cari said that rescuers had to be “very careful and move slowly, to avoid new collapses” as they searched for the two women.

Mayor Vincenzo Simonelli was at the scene and told reporters that the building appeared “crumpled up on itself,” adding it was “a very serious situation.”

Media reports said a gas leak could have caused the explosion that rocked the second floor of the building, which crumbled down, covering the lower floor with rubble.