Russian Orthodox priests have flown over a swelling river in a Soviet-era plane with an icon, praying for unprecedented floods to recede.

Rising rivers in Russia's southern Urals and western Siberia, as well as Kazakhstan, have flooded towns and cities and forced thousands to evacuate.

In the Kurgan region, priests boarded a small AN-2 plane with an icon of the "Mother of God Chimeyevskaya" for what they called a "procession in the air", praying for the massive Tobol river to stop overflowing.

The flight came ahead of the peak of floods in the area, expected in the second half of April.

The priests recited prayers as the plane swooped over the river, which has covered whole fields.

The Kurgan eparchy of the Orthodox church said the clergy had joined a monitoring flight with emergency services.

"During the flight, the clergymen read out a prayer to the Mother of God and performed a prayer service to overcome the natural disaster," it said in a statement published late Thursday.

Local Orthodox head Metropolitan Daniil said believers had asked him to fly over the zone with prayers.

"There is a tradition on Russian lands: to pray for people carry out processions -- on foot or by transport," he was quoted as saying in the church statement.

The priest said icons had traditionally helped Russia in times of trouble and will now help it deal with the the worst floods in decades.

He has instructed churches along the Tobol river to pray for the water to retreat.

Russia has evacuated around thousands of people from rising water -- but has said the number of flooded residential houses is higher.

Kazakhstan said it had evacuated more than 96,000.