Flooding is expected to peak on Monday in Russia's Kurgan region straddling the Tobol River near the border with Kazakhstan, as officials said waters maintained a sharp rise.
More than 7,100 people were evacuated on Sunday from several hundred residential buildings that had been flooded, state news agency RIA said, citing Russia's emergency ministry, as the waters threatened 62 settlements and 4,300 homes.
In neighbouring Kazakhstan, where more than 108,000 have been evacuated since floods began last week, waters submerged more than 1,000 additional homes in the city of Petropavlovsk on Sunday, forcing the evacuation of more than 4,500 people.
The Tobol rose 23 cm in the four hours to 6:00 am (0100 GMT) on Monday, the administration of the region, located at the confluence of the Ural mountains and Siberia, said on the Telegram messaging app.
The Tobol is typically frozen from November to April, with high water occurring in spring.
But this year's unusually large amounts of melting ice and snow have swelled rivers, bringing record floods in the Urals and Kazakhstan. In Kurgan, heavy rainfall has exacerbated the situation.
Earlier, Kurgan regional head Vadim Shumkov warned that flooding of the right bank of the Tobol, which slices the region south to north, and the low part of its left bank, would begin when waters reached a level of 600 cm.
Floods were also inundating homes in the Tomsk region in the southwestern part of Siberia, regional officials said on Telegram.
Almost 140 houses near the city of Tomsk, which is the regional administrative centre, were under water on Monday and 84 people were evacuated.