Storm Elias caused widespread flooding in the central city of Volos on Wednesday and left hundreds stranded in nearby mountain villages.
The city’s mayor said “it’s like the story of Noah’s Ark” as water levels rose rapidly within a few hours and a nearby stream that overflowed added to the flooding.
Military crews rescued elderly victims in dinghies or excavator buckets to lead them to safety. A total 280 people were evacuated to safe areas, the fire service said.
Prime Minister Kyriakos Mitsotakis said the natural disasters that have plagued Greece this summer “are attacks caused by climate change”.
Volos Mayor Achilleas Beos said power outages caused by the storm and flooding had plunged 80 per cent of the city into darkness.
“All of Volos has turned into a lake,” he told state television.
“People’s lives are in danger. Even I remained trapped, and 80 per cent of the city is without power.
“I don’t know where God found so much water. It’s like the story of Noah’s Ark.”
Authorities have stopped all vehicles from going onto the roads.
By Thursday morning, the storm had moved towards the island of Evia, a fire brigade official said. Some villages in northern Evia have been ordered to evacuate, state ERT TV said.
Storm Elias is the second major storm to hit the region since Daniel, the most intense storm to hit Greece since records began in 1930, battered the region for three days earlier in September.
It caused more than two billion euros (£1.7 billion) worth of damage to farms and infrastructure. Storm Daniel moved from Greece to Libya, where over 2,500 died in a huge flood in the city of Derna.
Many Volos residents said the authorities were still dealing with the aftermath of Daniel and had not been adequately prepared for another storm.
Residents in Volos used plastic buckets and brooms to push mud out of their homes and to try to protect their belongings.
Apostolis Dafereras, 83, has lived in a suburb of the city since 1955.
“I have never seen anything like this,” he told AP.
“The water came in and we were practically swimming,” Mr Dafereras said. “We stayed upstairs with our tenant.”
Authorities said the worst damage was reported around Volos and in northern parts of the nearby island of Evia, an area vulnerable to flooding due to the impact of massive wildfires two years ago.
The European Union has promised Greece more than two billion euros in financial support to cope with the damage caused by summer wildfires and the ongoing floods, while Athens is renegotiating the terms of other aid packages to direct funds toward climate change adaptation.
“Volos has been hit a second time with a storm of lasting duration. ... The state is with those who are struggling,” Prime Minister Kyriakos Mitsotakis said in Parliament.
“The positive course of the country has been overshadowed by natural disasters that are attacks caused by climate change.”
Mr Mitsotakis promised to rebuild infrastructure to a higher standard after roads, bridges and rail tracks were washed away in the floods.
But many flood victims in Volos told AP they felt unprotected.
“The situation wasn’t just handled in an amateur way,” city resident Pantos Pinakas said. “It was handled in a way (that was) extremely dangerous and reprehensible.”