Rescue teams have recovered the bodies of six people killed after a suspected gas leak triggered a blast that brought down a two-storey building in the historic Plaka district of Athens, local authorities said.

Documents and belongings found with four of the victims — two men and two women — indicated they were United States citizens, Greek state broadcaster ERT and other local media reported on Saturday. The other two victims were reportedly an elderly couple, a British man and a Greek woman, who lived on the building's second floor.

Two women were injured in an adjacent building, according to the fire department.

Athens Mayor Haris Doukas said the blast, which struck on Friday, was believed to have been caused by a major gas leak. Neighbouring buildings were damaged and evacuated as a precaution.

"The damage extends to the entire street as well as the street behind [the building]," Doukas said. "We are talking about an unimaginable catastrophe."

He said two adjoining buildings had suffered severe damage and might need to be demolished.

Greek daily newspaper Kathimerini reported that the four American tourists, who were due to check out of their accommodation at around 11:00am (08:00 GMT) to catch a flight back to the United States, never boarded their flight.

Residents had warned of gas leak risk.

A group of Plaka residents had alerted the municipality and the managers of the electricity and gas networks about the risk of short circuits or gas leaks in the area a year earlier, according to a letter published by Kathimerini. The group had called for a safety exercise to identify shortcomings in the emergency response system.

The citizen movement "We Remain Active" said on social media that a resident of the street where the explosion occurred had reported a smell of gas for several weeks and had warned the authorities.

A Greek police spokeswoman confirmed on ERT that residents had filed such a report, though the nature and origin of the substance had not yet been determined.

Plaka, one of Athens' oldest and most visited neighbourhoods, lies at the foot of the Acropolis, Greece's most-visited ancient monument.

Source: Al Jazeera (with AFP and AP)