The boat had about 200 passengers on board, coming from the neighbouring country of Niger. [Courtesy]

A boat ferrying about 200 people capsized in the northwestern Nigerian state of Kebbi on Wednesday but the number of casualties remains unclear, a state spokesman said.

The wooden boat capsized near Wara, a town on the shores of Kainji Lake, part of the Niger River, said Yahaya Sarki, a spokesman the governor of Kebbi.

It had about 200 passengers on board, coming from the neighbouring country of Niger.

"Bodies are still being recovered. We can't ascertain the number for now," Sarki said.

One survivor, Buhari Abubakar, said about 40 people have been rescued so far, though many of the other passengers, mostly women and children, are still missing.

Five bodies were recovered as of Wednesday evening, though local people expect more to wash up in the coming days, said Qasimu Umar Wara, a Wara resident.

"The boat was overloaded, he said. "My brother is among those missing. This is the worst boat accident that has happened in this water."

Many of the passengers were returning from a newly-discovered gold vein in Niger, Wara said.

"They usually go there in the evenings and return to Wara in the morning," he said. "Most of them are petty traders, food vendors and the local miners."