Rescuers in Sicily prepared late on Sunday for a second night of searching for possible survivors trapped under the rubble of collapsed buildings after a massive explosion probably caused by a gas leak.

Three people have been confirmed dead by Sicily's regional civil protection unit in the disaster that caused four residential buildings to topple to the ground on Saturday night in the southern town of Ravanusa.

Although two women were recovered alive from the debris early on Sunday after being found by sniffer dogs, six people remained unaccounted for as night fell. Rescuers had not heard signs of life from under the rubble since morning, authorities said.

Two women were recovered alive from the rubble in the southern town of Ravanusa after the collapse
Two women were recovered alive from the rubble in the southern town of Ravanusa after the collapse Vigili del Fuoco via AFP / Handout

"The search continues to the bitter end. We are searching in the hope of finding our six fellow citizens still alive," Ravanusa Mayor Carmelo D'Angelo said, according to Italian news agency AGI.

"We have the whole country on our side, and the best human and technological resources are in place. Hope will not be extinguished."

The blast, which occurred around 1930 GMT on Saturday, levelled four structures, including a four-story apartment building, in the central residential district of Ravanusa, a town of nearly 11,000 inhabitants, according to the civil protection unit.

Rescuers and sniffer dogs were still searching tfor survivors
Rescuers and sniffer dogs were still searching tfor survivors Vigili del Fuoco via AFP / Vigili del Fuoco

Television images broadcast throughout the day showed a mass of concrete rubble, wooden beams and mangled steel in a large empty space, with neighbouring buildings charred and damaged.

Firefighters had worked to extract the largest, heaviest materials from the site of the collapsed buildings in order to better access levels below, said Luca Cari, the spokesman for Italy's national firefighters.

"The problem is the huge quantity of rubble that we have to deal with to be able to advance," Cari told RaiNews24 television.

Rescuers search for the rubble for those still missing after the buildings collapsed
Rescuers search for the rubble for those still missing after the buildings collapsed Vigili del Fuoco via AFP / Handout

"The work is meticulous... we're moving debris but with great care in order to avoid provoking new collapses," he said.

Earlier in the day, Cari said it had been hours since the rescue teams had heard signs of life under the rubble.

"This certainly doesn't mean at all that we've given up hope but obviously with the time passing it doesn't play in our favour," he told SkyTG24 television.

The explosion was likely caused by a gas leak, authorities said
The explosion was likely caused by a gas leak, authorities said Vigili del Fuoco via AFP / Handout

Drone footage published on the national firefighters' Twitter page showed smoke still rising from the wreckage site, while adjacent buildings showed major signs of damage, including roofs half blown off.

The tall pile of rubble that firefighters and bulldozers sifted through included debris like a smashed car and destroyed domestic appliances like ovens, air conditioners and refrigerators.

A "huge shock wave" from the explosion was felt 100 metres (300 feet) away, said Salvatore Cocina, head of the regional civil protection unit.

An investigation had been opened into the cause of the explosion, which authorities said was most probably a gas leak. But the immediate priority, they said, was the ongoing rescue effort.

"The gas probably found a cavity in which to accumulate," the head of firefighters in the province of Agrigento, Giuseppe Merendino, told RaiNews24.

"This pocket of gas would then have found an accidental trigger: a car, an elevator, an electrical appliance."

Natural gas distributor Italgas said in a statement it had received no reports of gas leaks in the week leading up to the incident. 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, it said.

Soon after the explosion on Saturday night, which sent up tall flames at the site of the collapsed buildings, Ravanusa Mayor Carmelo D'Angelo appealed on Facebook for "everyone available who has shovels and bulldozers".

"There has been a disaster," he said.

Sicily, one of Italy's poorest regions, suffers from sub-standard and ageing infrastructure.

Many homes and other structures constructed in past decades were built using cheap, sub-par materials that make them more prone to collapse, often because of interference in building contracts by the Mafia.