Mayor Haris Doukas said the blast was caused by a massive gas leak, and neighboring buildings were evacuated.
Thirty firefighters and three dogs combed the rubble of the two‑story building, finding six bodies.
Two women were injured in an adjacent building on Lysikratous Street, according to fire brigades.
Greek state TV ERT confirmed the victims' identities and that the investigation into the gas leak is underway.
Tourists rescued from the neighboring building were all visitors, and the local pastor announced an outdoor Sunday service due to church damage.