Russia on Saturday said it had evacuated 4,000 people in the Orenburg region, in the southern Urals near Kazakhstan, due to flooding after a dam burst.
Emergency services had been working through the night after a dam burst in the city of Orsk, near the border with Kazakhstan.
The press service of the Orenburg governor said "4,208 people, including 1,019 children" had been evacuated and more than 2,500 homes were affected by the flooding after a dam burst on Friday following torrential rain.
Russia opened a criminal case for "negligence and violation of construction safety rules" over the burst dam, which was built in 2014.
Orenburg regional governor Denis Pasler said specialists assessed that the dam was built "for a different weight" and that the level of rainfall was "exceptional".
Authorities said the situation was difficult throughout the region, warning of a dangerous water level on the Ural river in the main city of Orenburg.
The mayor of the city of half a million people, Sergei Salmin, said authorities would forcibly evacuate people from flooded zones if they refused orders to leave.
He said the water level of the Ural river had risen to 855 cm and "will rise" further.
He named several districts of the city and nearby villages likely to be affected.
"The situation leaves you no choice. At night, the river can reach a critical level," he said. "I call on everyone in the flooded zone to leave their houses immediately.
"There is no time for convincing," he added, saying that "those who refuse to leave the danger zone voluntarily, we will forcibly evacuate with the help of police officers".
Kazakh President Kassym-Jomart Tokayev said the floods were one of the worst natural disasters in Kazakhstan in 80 years.
He called for authorities in the Central Asian country to be ready to help those affected.
Russian emergency services published images of rescue workers going through villages on boats and hovercrafts.
Several regions in the Urals and western Siberia have been affected by floods since the start of spring.
