Floods in the Russian city of Orenburg have raised water levels to two metres above critical, leaving just the roofs of some houses showing, Ednews reports via BBC.
The city's mayor urged many residents to leave home, as sirens sounded.
Levels in Orenburg are likely to peak on Friday, but floods are expected to spread through neighbouring regions over the coming days and weeks.
Kazakhstan has also been badly affected, with 100,000 people evacuated from their homes in the last week.
The flooding is being described as the worst to hit the region in 80 years.
Last week, several rivers - including the Ural, Europe's third-largest - burst their banks. A number flow back and forth between Russia and Kazakhstan.
High seasonal temperatures have led to rapidly melting snow and ice, compounded by heavy rains.
The Ural river reached 11.43m (37ft) in Orenburg on Friday. Authorities say that more than 10,000 people have been evacuated there, and 11,700 homes have been flooded.
Mayor Sergei Salmin has called for further mass evacuations in some districts.
"Leave your homes immediately. The situation is critical, don't waste time!" he said on his Telegram channel, adding that the sirens being heard in the city were not an exercise.
The city has a population of half a million and is about 1,500km (930 miles) south-east of Moscow.
Water levels have fallen in Orsk, further east and upstream of Orenburg. Orsk was badly affected last weekend after a dam burst and saw rare public protests against low compensation offers and perceived failures by local authorities to save the dam.
From Orenburg the Ural flows through northwest Kazakhstan and into the Caspian Sea.
The Ishim and Tobol rivers are also reaching dangerous levels, and are only predicted to peak around 23-24 April.
Floodwaters are threatening a whole swathe of northern Kazakhstan and many dams and reservoirs there are filled to capacity.
In Petropavl on the Ishim river, in North Kazakhstan region, a local reservoir was threatening to overflow, potentially flooding a major road between two Russian cities - Chelyabinsk and Novosibirsk.
Meanwhile the Russian village of Kaminskoye has been evacuated after levels in the Tobol rose 1.4m overnight, regional governor Vadim Shumkov said.
Kurgan, the regional capital and city of 300,000, lies downstream and is also thought to be at risk.
