The floods, among the worst Turkey has experienced, brought chaos to northern provinces just as authorities were declaring wildfires that raged through southern coastal regions for two weeks had been brought under control.
Torrents of water tossed dozens of cars and heaps of debris along streets, with bridges destroyed, roads closed and electricity cut to hundreds of villages. Media reports said President Tayyip Erdogan was to visit the region on Friday.
"This is the worst flood disaster I have seen," Interior Minister Suleyman Soylu told reporters late on Thursday after surveying damage which extended across the provinces of Bartin, Kastamonu and Sinop.
"The risk that our citizens face is high... There is a lot of damage to infrastructure."
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Twenty-five people died as a result of floods in Kastamonu and another two people died in Sinop, the country's Disaster and Emergency Management Directorate (AFAD) said.
Sinop Mayor Baris Ayhan put the death toll in his province at three, adding that authorities could not contact another 20 people. He urged the government to declare it a disaster zone.
"The infrastructure in Ayancik (district) has completely collapsed. The sewage system is destroyed. There is no electricity or water," he told Reuters.
The floods and the fires, which killed eight people and devastated tens of thousands of hectares of forest, struck in the same week that a U.N. panel said global warming is dangerously close to spiraling out of control, and warned that extreme weather would become more severe.
Footage of the flood's first moments in Kastamonu's Bozkurt district showed the river there overflowing in a fast-moving deluge which tore up trees and dragged away vehicles.
More than 1,700 people were evacuated from flood-affected areas, some with the help of helicopters and boats, AFAD said.
Helicopters lowered coast guard personnel onto the roofs of buildings to rescue people who were stranded as flood water swept through the streets, footage shared by the Interior Ministry showed.
The deluge damaged power infrastructure, leaving about 330 villages without electricity. Five bridges had collapsed and many others were damaged, leading to road closures, AFAD added. Parts of the roads were also swept away.
Turkey's meteorology authority said further heavy rain was expected in the central and eastern Black Sea region and warned of the risk of further floods.