Twelve children and a villager have been killed in a hippopotamus attack on a boat near Niger's capital Niamey earlier this week, officials say.

The students, aged 12 to 13, died when their boat transporting them across the Niger River was flipped by the hippopotamus on Monday.

A number of students in the West African nation take such boats to attend school on the other side of the river.

"Ultimately it was 12 students, including seven girls and five boys, who died after the attack," minister of secondary education Aichatou Oumani said.

A villager on the same boat was also killed, according to an official in Libore, the village near the site of the accident.

An earlier toll had spoken of two deaths, 11 missing and five survivors. At least 18 people were aboard the boat, mostly students.

"We have already given the order for the animal to be identified and killed," governor of the Tillaberi region Hassoumi Djabirou said.

Game wardens shot dead a hippopotamus last year after it killed a teenager in Niamey.

Hippopotamus with young in tow are the most aggressive, even attacking cattle that come to graze on the banks of the Niger River, experts said.

AFP