More than 90,000 people have been evacuated from rising rivers in northern Kazakhstan and Russia's southern Urals, which are witnessing one of their worst flood disasters in decades.

Rivers have been overflowing for days in 10 regions of Kazakhstan, as well as in Russia's western Siberia and Orenburg regions, flooding entire cities and villages. 

Both Moscow and Astana have introduced a state of emergency. 

"Since the beginning of the floods, more than 86,000 people have been rescued and evacuated," the Kazakh government said on Tuesday. 

It said 3,365 residential buildings had been flooded in five different regions of the vast Central Asian country. 

The government said it was taking humanitarian aid to affected areas. 

President Kassym-Jomart Tokayev has called the floods one of the worst natural disasters in 80 years. 

In neighbouring Russia, emergency services said on Tuesday 10,550 residential buildings were flooded, mostly in the Orenburg region, where more than 6,500 people have been evacuated. 

The Ural river has almost entirely flooded the city of Orsk and is now reaching dangerous levels in the main city of Orenburg. 

The river had risen by 25 centimetres (10 inches) in Orenburg over the last 24 hours, authorities said on Tuesday. 

- Villages under water -

The peak of the flood in Orenburg -- a city of 550,000 people -- is expected on Wednesday.

Mayor Sergei Salmin said it would be "unprecedented." 

The mayoral office said on Tuesday the situation was "critical" in eight villages near Orenburg. 

Rivers in western Siberia's Kurgan and Tyumen regions are also swelling.

In Kurgan, a city near Kazakhstan, authorities said on Tuesday 689 people have been evacuated away from the overflowing Tobol river. 

The mayoral office in Kurgan -- a city of around 300,000 people -- said the floods could reach the local airport. 

In one village in the Kurgan region, Zverinogolovsk, the water levels of the Tobol river rose 74 centimetres in just two hours, Russian media reported. 

Russian Emergency Situations Minister Alexander Kurenkov travelled to the Orenburg region on Tuesday.

His ministry said he would then visit the Kurgan and Tyumen regions. 

The ministry released a video of Kurenkov flying over flooded zones in a helicopter, showing vast expanses of water stretching to the horizon and villages submerged.