Four members of the same family, including two young children, have died in a gas explosion in southern Italy.

Their two-storey home in the town of Saviano, near Naples, partially collapsed in the blast, killing the siblings – a boy and a girl – as well as their mother and grandmother.

The father and a newborn baby were recovered from the rubble alive, Italian firefighters said.

He remains in hospital in Naples in serious condition, while the baby’s injuries are not life-threatening, local media reported.

The Vigili del Fuoco, Italy’s fire service, reported that the parents and three children lived on one floor of the property, while another woman – said to be the grandmother – lived on the floor above.

“Firefighters recovered the father and a newborn baby alive, entrusting them to the care of the health workers on site, while they could do nothing for the two children, a boy and a girl, whose bodies were unfortunately recovered lifeless,” The Vigili del Fuoco said in a statement.

While authorities have not confirmed the ages of the children, local media reported that they were four and six.

The explosion occurred at around 07:00 local time (06:00 BST), the Vigili del Fuoco said.

Firefighters found the children and father in the morning, then spent the day searching through the rubble, not locating the mother until 16:45.

Firefighters’ spokesman Luca Cari told reporters during the day that rescuers had to be “very careful and move slowly, to avoid new collapses” as they searched, the Associated Press reported.

Search and rescue teams, operating with sniffer dogs, continued the search for the grandmother into the night, announcing they had found her and had wrapped up the search at 01:00.

Investigations are continuing into the exact cause of the building’s collapse, but early theories suggest the house collapsed after a gas explosion.

More than 60 civil protection volunteers joined the rescue efforts, the Campania region authority wrote in a post on Facebook.

Images shared by the fire service showed rescue teams working through the rubble of the destroyed building through the night.

Drone footage of the scene showed two gaping holes in the roof of the building, which was partially collapsed.