A woman and her daughter died, and 4,000 people had to be evacuated when a dam wall broke in Russia's Dagestan republic following heavy rains, the Civil Protection Ministry reported on Monday.

Around 2,000 homes were flooded in the Derbent region on the Caspian Sea. The bodies of the woman and her daughter were found, but other people remain missing.

Makhachkala, capital of Dagestan, has also been hit by flooding, with apartment blocks threatened by collapse, according to regional news website Golos Dagestana (Voice of Dagestan).

Video clips on social media showed entire buildings sinking beneath the water, along with a collapsed bridge on the Kavkaz route that is of strategic significance for the region.

The regional authorities have set up emergency shelters, and helicopters are being used. The ministry said that further rains could be expected in the region, with localized cloudbursts and winds gusting up to 120 kilometres per hour. Landslides could also be expected, it said.

Heavy rains have hit the Northern Caucasus region since the end of March. Flooding of power substations has led to outages in almost 20 districts in Dagestan.

A state of emergency has been called in Makhachkala, Khasavyurt, Kaspiysk and Derbent.

Flooding at the end of March led to more than 3,300 people being evacuated, amid reports of 3,500 flooded homes. At the time, authorities put damage at the equivalent of $50 million, but the figure is now likely to be much higher.