Floods devastate northern Turkey, killing at least 27, and leaving dozens missing.

Flash floods in northern Turkey have killed at least 27 people, and many other local residents missing and hundreds homeless, as rescue workers scrambled to evacuate those affected by the disaster and reach villages that had been cut off by the waters and lost power.

In the province of Kastamonu, at least nine people, including five young children, were still missing. Eight were from the same extended family in the town of Bozkurt, including four children.

Turkish authorities have yet to announce an exact number of missing. But accounts from residents of areas affected by the disaster suggest a far worse picture than the one portrayed in official statements.

“Thank God we managed to leave that house, but there are many people who couldn’t,” Sumeyra Ergin Felek, one resident, said in a video posted on Instagram. “There are many people under the ruins.”

The Turkish broadcaster NTV said that more than 100 people were unaccounted for, a figure officials neither denied nor confirmed.

Video shared on social media showed bodies washed up on the coastline alongside tree branches and other debris caught up in the floodwaters.

“The number of casualties may increase,” said Hasan Baltaci, an opposition lawmaker who was in Bozkurt, which has a population of about 9,000.

“They recently pulled out a body from a grocery store, although it was supposed to have been evacuated,” Mr. Baltaci said.

The missing from the extended family in Bozkurt included 12-year-old twin girls and their grandparents, as well as two younger children and their two aunts, a relative, Fatih Karaalioglu, said by telephone.

Arzu Yucel, the mother of the twins, said the family had only been warned to move their cars to higher ground as a precaution against flooding.

Ms. Yucel, speaking in a video interview to the Demiroren news agency, said she left the apartment block next to the Ezine river where the family has apartments, on Wednesday to move the car. She became trapped by the rising waters and had to take shelter on the staircase of a nearby building.

For five hours, Ms. Yucel said, she was able to wave to her children on one of the balconies of the apartment block. But then the block collapsed.

“My eyes saw everything, we couldn’t do anything,” Ms. Yucel said.

“They told us to move the cars, not to save our lives,” she said. “I could have saved them.”

Ramazan Yucel, her husband, returning from Istanbul, arrived in the disaster area early on Thursday alongside some rescue workers, and after reaching the collapsed building by boat, worked fruitlessly to find survivors, said Mr. Karaalioglu, the relative.

“It is a meter-deep mud, and the Ezine still flows strongly,” he said, referring to the river, which he said had flooded more than 300 feet into the city.

Flooding is common in many of the Turkish cities adjacent to the Black Sea, partly because of the building of structures in river beds and the mismanagement of rivers that has narrowed natural channels, according to experts.

“It is extremely dangerous to open flood plains to construction. This is why the building in Bozkurt collapsed,” one geologist, Ramazan Demirtas, said in a tweet. “It is the humans who are guilty, narrowing down the river bed to 15 meters from 400, and opening it to construction,” he said in another tweet.