Flooding after a rainstorm late Wednesday washed away or submerged at least 50 homes in the city and 10 people remained missing on top of the confirmed dead, an emergency management official said.
"The surging flood water submerged and washed away over 50 residential houses with their occupants," said Abdullahi Baba-Arah, director general of the Niger State Emergency Management Agency (SEMA).
Divers and volunteers rescued one woman and her two children, who were being treated in hospital for "wounds and shock".
Nigeria is hit by flooding every rainy season, which runs between May and November.
The floods are largely caused by inadequate drainage, the construction of homes on waterways, and the dumping of waste in drains and water channels.
The Nigerian Meteorological Agency had warned of possible flash floods in 15 of Nigeria's 36 states, including Niger state, between Wednesday and Friday.
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Nigeria's rainy season is just getting started for the year. Scientists warn that climate change is already fuelling more extreme weather patterns.
Flooding, usually caused by heavy rains and poor infrastructure, wreaks havoc every year, killing hundreds of people across the West African country.
In 2024, more than 1,200 people were killed and 1.2 million displaced in at least 31 out of Nigeria's 36 states, making it one of the country's worst flood seasons in decades, according to the National Emergency Management Agency (NEMA).
More than 1.4 million hectares (3.5 million acres) of farmland were also destroyed last year, said NEMA.
Floods which struck the country two years earlier, in 2022, killed more than 500 people, reports BSS.
Niger state is in a precarious situation as it is already grappling with violence from jihadists as well as gangs known as "bandits" who raid villages, kill and abduct residents.