Families were swept away in a torrent of water and scores were feared dead in flooding from a dam collapse in northwest Nigeria, witnesses and state radio said Sunday.

The dam collapsed on Saturday after heavy rains apparently overwhelmed the structure, according to state-owned Radio Nigeria.

The station said about 40 people were feared dead and 500 houses were washed away, but there was no independent confirmation of the figures. State police Commissioner Mustapha Abubakr said three deaths had been confirmed and survivors were being sheltered in a primary school. Thirty houses were destroyed, he said.

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One witness said he counted seven bodies. Johnson Enokola, 39, a resident of the area, also said most of the houses around the bank of the dam were washed away.

Another resident, 35-year-old Easter Peter, said by telephone from Zamfara state: "I have never seen anything like this in my life. Whole families were washed away by the water into the dam." The dam is located outside Zamfara's capital city of Gusau.

There was also heavy flooding in neighboring Sokoto state this week, destroying hundreds of houses and polluting the drinking water of thousands of people, officials said.

The head of the Sokoto state water board said that flooding in Sokoto had been exacerbated by the failure of a separate dam. That structure failed to release floodwaters due to a buildup of sediment in the dam outlets, said Dahiru Yusuf Yabo. He said he did not know if the two floods were connected.

The two flooded areas are about a two hour drive apart, Yabo said.

"The water is continuing to rise and flood farmlands," Yabo said of Sokoto. "Most people had time to flee but they had to abandon most of their belongings."

The floodwaters contaminated wells of nearly 10,000 people, Yabo said.

"There is a risk of disease, so we are dispatching people with water treatment kits," he said.

Ibrahim Farinloye, a spokesman for the National Emergency Management Agency, said teams of rescue workers had been dispatched to both states.