Renewed flooding of the Niger river threatens Niger's capital Niamey and parts of the west of the country, local and regional authorities warned Thursday.

Previous floods in August and September claimed almost 70 lives across the impoverished west African country and made tens of thousands homeless.

"We will be inundated" as of December 5, Niamey governor Aichatou Kane Boulama told a press briefing. She stressed that the consequences would include the flooding of 400 hectares (988 acres), 40 of them in residential areas.

Water has already begun to swamp some low-lying parts of Niamey, Kane Boulama added, saying that "the most urgent thing is to rehouse families".

The floods will be exceptional because of heavy rain late in the year, the Niamey-based Niger Basin Authority, which groups nine countries, warned on its website.

The third-longest river in Africa, the Niger has a basin of more than two million square kilometres (772,000 square miles), which is home to more than 100 million people, from Nigeria to Guinea.