The blast on Saturday evening in the southern town of Ravanusa levelled four structures, including a four-storey apartment building, in the central residential district of the town of nearly 11,000 inhabitants, according to the civil protection unit.
The two people missing were said in media reports to be a father and son aged 88 and 59 years old.
Two women were recovered alive from the debris early on Sunday, but rescuers have not heard further signs of life.
Rescuers on Monday found four more bodies in the rubble raising the official death toll to seven, officials said.
Pope Francis sent his condolences and “heartfelt closeness” to the victims and their families following the blast, which left over 100 people homeless.
He also expressed his “appreciation for those who have done their best in rescue operations”, during which dozens of firefighters have combed night and day through the rubble with the help of sniffer dogs.
🔴 #Ravanusa, #crollo palazzo: terza notte di lavoro per i #vigilidelfuoco, con la luce delle fotoelettriche sono proseguite senza sosta le operazioni di ricerca delle ultime due persone disperse tra le macerie. 40 #USAR e 9 #cinofili in azione [#14dicembre 9:00] pic.twitter.com/czdznxisIW
— Vigili del Fuoco (@emergenzavvf) December 14, 2021
An investigation has been opened into the cause of the explosion, which authorities said was most probably a gas leak.
Local resident Calogero Bonanno said “neighbours had told me there was a smell of gas”.
“I heard a tremendous roar, as if a bomb had gone off or a plane had crashed into the house,” he was cited as saying by Italian media.
“Then the window frames exploded. We immediately went down to the street, there was fire everywhere, rubble all around,” he said after fleeing along with his wife, three children and in-laws.
“It’s a miracle we’re alive”.
Natural gas distributor Italgas said it had received no reports of gas leaks in the week leading up to the incident, despite local residents reporting hearing complaints of a smell of gas.
No construction work was under way in the section of pipeline affected in the blast and the town’s distribution network was fully inspected in both 2020 and 2021, Italgas said.
Italian newspaper La Repubblica said the town’s gas pipelines – installed 36 years ago – were among the oldest in Italy, and ran through unstable ground susceptible to soil erosion and landslides.