Eleven people were killed on Tuesday as flash floods hit Turkey, Greece and Bulgaria, officials said.
Two died in Istanbul and 12 others were injured after heavy rain transformed the city's streets into fast-flowing rivers in the Basaksehir and Kucukcekmece districts, the Istanbul Governor's Office said.
More were feared dead.
The surging flood waters affected more than 1,750 homes and businesses in the city, according to the Governor’s Office.
They included a line of shops in the Ikitelli district, where the deluge dragged parked vehicles and mud into furniture stores, destroying the merchandise, DHA reported.
The floods also engulfed a parking area for containers and trucks on the city's outskirts where people found safety by climbing on the roof of a restaurant, Turkish media reported.
Three other people were killed and three others were missing in the north-western city of Kirklareli, near the border with Bulgaria, Turkey's emergency service said.
The storm partially flooded an Istanbul subway station and forced the evacuation of dozens of people from a city library, local media reports said.
Television and social media images showed rushing water sweeping away cars and city market stalls.
The rain followed a particularly dry summer during which water levels in the city's reservoir of the city of 16 million people fall to nine-year lows.
Turkish Interior Minister Ali Yerlikaya said people were missing after the floodwaters swept over the campsite in Kirklareli. Mr Yerlikaya said about 12 campers were at the site at the time.
Search teams had located two bodies, he said on X, the social media platform formerly known as Twitter. “The search and rescue efforts for the missing continue uninterrupted,” he said.
Television footage showed rescuers carrying a young girl and an adult to safety from waist-high waters. The rains also damaged and forced the closure of a main road, HaberTurk television reported.
Heavy rain also hit neighbouring Greece and Bulgaria, causing floods that killed at least five people.
In Greece, police banned traffic in the central town of Volos, the nearby mountain region of Pilion and the resort island of Skiathos as record rainfall caused at least one death, channelled thigh-high torrents through streets, and swept cars away.
The fire department said one man was killed near Volos when a wall buckled and fell on him while at least five people were reported missing, possibly swept away by floodwaters.
Authorities sent text message alerts in several other areas of central Greece, the Sporades islands and the island of Evia warning people to limit their movements outdoors.
Streams burst their banks and swept cars into the sea in the Pilion area, while rockfalls blocked roads, a small bridge was washed away, and many areas suffered electricity cuts. Authorities evacuated a retirement home in the city of Volos as a precaution.
Greece’s weather service said one Pilion region village received 75.4cm of rain late on Tuesday, by far the highest level recorded since 2006.
The average annual rainfall in the Athens region is around 40cm, it said.
Heavy rain is expected to ease on Wednesday afternoon, said Vassilis Kikilias, Greece's Minister of Climate Change and Civil Protection.
People in affected areas have been advised to stay indoors.