Emergency rescue workers and firefighters were searching parts of northern and western Athens on Thursday night after flash floods in the capital left at least one person dead.
The rescue teams were looking for others who may have been swept away or drowned following fierce rain in the capital. Some 560 people were to remain on duty overnight.
During the day, the fire service received more than 800 calls to help pump water out of basements as a result of the flooding.
A 41-year-old man lost his life in Acharnes, northern Athens, after his car became trapped. Passers-by were able to remove the man and his 71-year-old mother from the vehicle but he was pronounced dead at the hospital.
His mother survived but remained under observation last night.
A three-story apartment block in Kamatero, western Athens, collapsed as a result of subsidence. The building had been vacant since last year, when the regional authority deemed it unsafe as it had been built next to a former streambed.
The weather, which included gale-force winds, caused difficulties in other parts of Greece.
Six aircraft were unable to land at Makedonia Airport in Thessaloniki due to the blustery conditions. Four were rerouted to Athens, while the other two had to land in Sofia, Bulgaria.