At least six people have died and more than six were missing on Thursday after Storm Daniel swept across central Greece, causing landslides, destroying roads and bridges and carrying away dozens of cars.
Prime Minister Kyriakos Mitsotakis postponed an annual economic speech scheduled for this weekend to visit areas hit since Monday by torrential rain that has flooded homes and destroyed key infrastructure.
"The state mechanism's absolute priority right now is the rescue and evacuation of people from the areas affected," government spokesman Pavlos Marinakis told a media briefing.
"Our country is facing for the third day a phenomenon unlike any other we have seen in the past."
Mr Marinakis said the recently re-elected Mr Mitsotakis's main economic policy speech would be held in the middle of next week instead of Saturday.
The mainland port city of Volos, the surrounding mountainous Pelion area and the cities of Karditsa and Trikala were among the worst-hit areas.
The heavy rainfall came days after a deadly two-week wildfire in the north, which authorities said was the most extreme on record.
The rain has turned many villages in the low-lying area of Karditsa, in the mainland Thessaly plain, into a lake.
Civil Protection Minister Vassilis Kikilias said on Thursday that six people had been reported missing in the Karditsa area.
The fire brigade said the bodies of two elderly women were recovered from a house at the community of Astritsa near Karditsa on Thursday.
The body of a man had been found in the town of Domokos earlier in the day.
Reuters footage showed houses submerged in floodwater in the Trikala region.
In the town of Palamas, near Karditsa, dozens of people were trapped inside their flooded homes, Mayor Giorgos Sakellariou told Open television.
Residents speaking to local media called for help and food supplies.
A fire brigade helicopter lifted people from the village of Agia Triada, where at least 20 had been trapped, the government said.
Since Tuesday, 820 people have been evacuated across the country, 750 of them in the Thessaly region.
A fire brigade official said that emergency crews assisted by the army and coastguard used lifeboats in an effort to reach the storm-hit villages in Karditsa, where water was two metres deep.
"Operations are been carried out very carefully as flood debris obstructed the boats, while, in other cases, the power of the water does not allow us to approach," fire brigade spokesman Vasilios Vathrakogiannis told a briefing.
Crews will continue going from door to door to rescue people throughout the night, while 3,000 meals and water will be handed out across Karditsa and Trikala, Mr Kikilias said late on Thursday.
The EU has been in contact with Greece to rally support, EU Commission President Ursula von der Leyen said on X, formerly known as Twitter.
British travel company Jet2 said on Wednesday it was cancelling all flights and holidays to the Aegean island of Skiathos, the closest to Volos, up to September 12 because of the weather.
Flash floods in Greece in 2017 killed 25 people and left hundreds homeless.
