Flood waters were rising in two cities in Russia's Ural mountains on Sunday after Europe's third-longest river burst through a dam, flooding at least 10,000 homes and forcing thousands of people to flee with just their pets and a few belongings.

Some of the worst floods in decades have hit a string of Russian regions in the Ural Mountains and Siberia, alongside parts of neighbouring Kazakhstan in recent days.

The Ural River, which rises in the Ural Mountains and flows into the Caspian Sea, swelled several metres in just hours on Friday due to melt water, bursting through a dam embankment in the city of Orsk, 1,800 km (1,100 miles) east of Moscow.

The mayor of Orsk, Vasily Kozupitsa, was quoted by Russian news agencies as saying a second river in the town, the Yelshanka, had also burst its banks. Measures were being undertaken to evacuate residents from affected areas.

More than 6,100 people have already been evacuated from the city of 230,000, according to local authorities. Fifteen of 40 schools in the school had been flooded.

Footage published by the Emergencies Ministry showed people making their way through neck-high waters, rescuing stranded dogs and travelling along flooded roads in boats and canoes.

State news agency TASS reported that six adults and three children had been hospitalised in Orsk, but their condition was not life-threatening.

Agencies quoted authorities as saying the Samara River in the town of Buzuluk, further west in Orenburg region, was also rising quickly. Measures were taken to keep residents safe.

President Vladimir Putin ordered Emergencies Minister Alexander Kurenkov to fly to the region. The Kremlin said on Sunday that flooding was now also inevitable in the Urals region of Kurgan and the Siberian region of Tyumen.

Putin had spoken to the governors of the regions by telephone, the Kremlin said.

In Kurgan city, which has a population of 310,000, authorities ordered residents of one riverside neighbourhood to evacuate urgently, saying that flood waters would soon arrive in the city.

The Orenburg region's governor, Denis Pasler, said the floods were the worst to hit the region since records began.

He said that flooding had been recorded along the entire course of the 2,400-km (1,500-mile) Ural River, which flows through Orenburg region and then through Kazakhstan into the Caspian Sea.

Russian media cited Orenburg region authorities as estimating the cost of flood damage locally as around 21 billion roubles ($227 million) and saying that flood waters would dissipate only after April 20.

In Kazakhstan, President Kassym-Jomart Tokayev said on Saturday the floods were his country's largest natural disaster in terms of scale and impact for 80 years.

North Korea leader Kim Jong Un expressed sympathy to Putin about the flood, state media KCNA said, underscoring stronger ties between Moscow and Pyongyang after the leaders met last year.

"Our people will always be with the Russian people," Kim said.