Russian authorities on Tuesday began fresh evacuations from towns and villages in western Siberia threatened by devastating floods that have swept the region and neighbouring Kazakhstan.

The floods have forced thousands to flee and are expected to peak this week on the Tobol and Ishim rivers.

The governor of the Tyumen region, Alexander Moor, said emergency services had begun "urgent evacuations" from towns expected to be inundated.

"Pack your valuables. Leave now for a safe place, to relatives or to a temporary accommodation centre," Moor said on social media.

In Tyumen, the level of the Ishim river reached "critical" levels of 808 centimetres in some areas, local authorities said.

Some 67,000 residents of Ishim, a town with the same name, were urged to flee via text message.

In the neighboring Kurgan region, the level of the Tobol river rose by 111 centimetres over the last day, reaching 742 centimetres, authorities said.

The residents of 21 towns and villages have been asked to leave their homes.

Russian Emergencies Minister Alexander Kurenkov and the governor of Kurgan, Vadim Shumkov, inspected flooded regions by helicopter on Tuesday, the ministry said.

In the Orenburg region, which has been at the heart of the flooding in recent days, the level of the Ural river has dropped, authorities said.

Over the past 24 hours, water has receded from around 1,000 flooded homes, regional officials said.

The town of Orsk, where the situation recently improved after heavy flooding last week, was again under threat after water overflowed from a dam.

Authorities in Kazakhstan reported last week that over 100,000 people were evacuated over the rising water levels.

The floods have been caused by heavy rainfall combined with rising temperatures and increased melting of snow and ice.