The cause of the explosion was not immediately clear, but local media said a gas leak was suspected.
Rescue crews with a sniffer dog were searching the rubble for potentially missing people, the fire department said.
The cause of the blast was being investigated (Petros Giannakouris/AP)
Residents said that two people lived in one of the building’s apartments, and there were media reports that three tourists may have been staying in a short-term rental apartment also in the building.
The fire department said the explosion occurred in an old two-storey building in the Plaka district, the historic part of Athens that lies at the foot of the Acropolis hill, Greece’s most visited ancient monument.
The building collapsed, while neighbouring buildings were also damaged.
The fire department said the explosion occurred in an old two-storey building in the Plaka district (Petros Giannakouris/AP)
Firefighters rescued two women from an adjacent building, with police saying both were being taken to hospital. Local media said a passer-by was also slightly injured by the blast.
Police cordoned off the area as rescue crews and the sniffer dog moved slowly over the rubble. The fire department said the search and rescue operation was still ongoing several hours after the explosion.
“An elderly couple lived upstairs, on the second floor,” resident Andreas Martzaklis said, adding that he did not know whether they had been inside at the time of the explosion or managed to get out. He said one apartment in the building that collapsed had been operating as a short-term rental apartment, while the others were privately owned.
“Who got out of the building that is destroyed, we don’t know anything,” said Mr Martzakis, who lives in a nearby building and heard the blast while he was drinking his morning coffee.
Police cordoned off the area (Petros Giannakouris/AP)
The people rescued by the fire department from the adjacent building were all tourists, he added.
The pastor from a nearby church said this Sunday’s service would be held outdoors because of damage to the church from the explosion.
“Of course we went in. It was heartbreaking. From the bottom to the top, there is no window that has not been broken,” Giotis Kantartzis, pastor of the First Greek Evangelical Church in Athens, said.
Video footage from the scene showed rubble strewn across the street, with parked cars smashed by falling debris.