A powerful gas explosion caused a building to collapse in Plaka, the historic and popular tourist district of the Greek capital, Athens, killing at least six people, including four U.S. citizens.

Rescue teams recovered the bodies from the rubble of the two-story collapsed building on Saturday (September 26), according to a report by the Qatar-based news outlet Al Jazeera.

An examination of recovered documents and personal belongings confirmed that the four deceased American citizens were two men and two women who were staying in the building as tourists.

The other two victims were an elderly couple residing on the second floor—a British man and a Greek woman. Two people in an adjacent building were also injured in the incident.

Athens Mayor Haris Doukas stated that the catastrophic blast likely stemmed from a major gas leak.

The intensity of the explosion completely leveled the building and severely damaged several surrounding structures.

Out of safety concerns, buildings in the affected area have been evacuated.

Meanwhile, the Greek daily Kathimerini reported that the four American tourists were scheduled to catch a flight back home on Friday morning.

However, they fell victim to the disaster before they could check out.

Local residents alleged that the area had long faced risks of gas leaks and short circuits.

Despite repeated warnings to municipal authorities and the utility company, no visible action was taken.

Police are currently investigating to determine the exact cause and precise source of the gas explosion.