At least six people have died and more than six were still missing after storm Daniel swept across central Greece, triggering landslides, destroying roads and bridges and carrying away dozens of cars.
The fire service announced that they had found the bodies of two elderly women, as well as a shepherd washed away by the flood waters.
Emergency services worked alongside the army to get to the stranded residents, while more villages had to be evacuated after flooding damaged a dam.
Fierce storms have battered Greece, Turkey and Bulgaria following a period of extreme heat and devastating wildfires - the kind of extreme weather climate experts say is becoming more frequent because of human-induced climate change.
The downpour, from Monday evening into Tuesday, hit the central region of Thessaly, 300km north of Athens.
Flooding affected the port city of Volos, and the towns of Karditsa and Tikala further inland and several villages, after more than a year's worth of rain fell there in 24 hours.
Houses sank under water, while cars and even a bridge were washed away.
Night-time rescue operation
Summarising the situation in Thessaly, Civil Protection and Climate Crisis Minister Vassilis Kikilias told reporters that some 67 people had been rescued from the villages near Karditsa.
"Rescuers and rescue boats and all available teams with artificial lighting will continue house-to-house rescues in the stranded villages during the night," he said.
Operations were complicated because of a breached dam between Trikala and Karditsa, along a tributary of the flooded River Pinios.
While ten helicopters had been operating, including three from the army, they would have to stop overnight.
Austria's foreign ministry said that two of its citizens had gone missing in the area.
The plain of Thessaly, the country's largest "has been transformed into a vast lake", Dimitris Theodorou, a retired farmer from the village of Farkadona said.
"You can't even see the cornfields, that are two, to two-and-a-half metres high," he added.
A bridge over the River Enipeas near the town of Farsala was swept away by the floodwaters.
'Trapped in their houses'
Earlier, ERT television broadcast images of a Super Puma helicopter helping evacuate an elderly person.
A total of 480 firefighters with 195 vehicles are taking part in these operations complicated by the high levels of the floodwaters.
"For the third consecutive day, the country is facing an unprecedented phenomenon" with floodwaters making it difficult to reach some towns and villages, government spokesman Pavlos Marinakis told journalists.
Emergency services had sent teams of divers and lifeboats to help with the rescue operation, he added.
Private TV channel Skai showed footage of houses under water in Palmas in the Karditsa district of Thessaly.
"The inhabitants are trapped in their homes without any help," the city's mayor, Giorgos Sakellariou, told the channel, adding that the floodwater was up to two metres high.
Prime Minister Kyriakos Mitsotakis postponed a visit to northern Greece, setting up an emergency coordination unit in Larissa, one of the main towns in Thessaly.
He also postponed his weekend visit to the Thessaloniki International Trade Fair, where he had been due to give the annual keynote speech, present the government's four-year plan and hold a major news conference.
The heavy rains and flooding follow devastating fires in Greece this summer that killed at least 26 people.
"Unfortunately, we are moving from one natural disaster to another in Greece," European Commission spokesman Balazs Ujvari told reporters in Brussels.
The EU's civil protection mechanism stood ready to assist, he added.
Irish rally competitors caught in storm
Irish crews preparing to compete in a World Rally Championship event in Greece have been caught in the heavy rain and flooding that has hit the country.
The Acropolis Rally is based in the Greek city of Lamia, around 200km north west of Athens, started today.
Organisers have changed the planned itinerary for the rally in the interest of safety.
Eamonn Kelly from Co Donegal and his co-driver Conor Mohan from Co Monaghan are two of the five Irish competitors entered in the rally.
"It's really bad," said Mr Kelly. "There has been weather warnings put out to people in the local area, different curfews and stuff just because of how bad the flooding is."
He said that a number of rivers have burst their banks making national roads impassable, adding: "It’s made things very difficult even for the locals never mind us."
Mr Mohan said that he had "never seen rain like it".
"It has been non-stop rain. It hasn’t really stopped. There’s been up on ten millimetres of rain at some stages throughout the day and serious big floods to be fair," he said.
