Some 100,000 people across the arid west African country of Niger will likely be hit by massive flooding this year, the United Nations warned on Tuesday.

Heavy rains are set to hit multiple regions in the poor country and may affect about 105,000 people, the UN's Office for the Coordination of Humanitarian Affairs (OCHA) said in a statement.

"A comprehensive contingency plan" will be put in place as soon as about a tenth of the total population of 18 million is affected, the UN agency added.

OCHA said it has begun to gather resources to help possible victims. Local authorities are meanwhile building levees along the Niger River's embankment to protect the thousands living in the capital Niamey, state media reported.

The river, Africa's third largest, has a flood basin of over two million square kilometres (770,000 square miles) which is home to more than 100 million people from Guinea to Nigeria.

Climate change has wreaked havoc in Niger, bringing floods, droughts, spikes in temperature and food shortages -- buffeting the lives and livelihoods of millions of the country's farmers.

Flooding in 2012 killed more than 100 people, affected more than half a million Nigeriens and caused at least 135 million euros ($145 million) worth of damage, according to the disaster prevention office.

Floods similarly killed dozens of people and affected hundreds of thousands in 2014 and 2015.

Niger's inhabitants are no strangers to hardship and the landlocked former French colony is already one of the world's least developed countries, ranking 187th on the UN Human Development Index.

Global warming is only worsening the problems, with the steadily encroaching desert now covering three-quarters of Niger.

The sands are encroaching on the Niger River, threatening the survival of several millions living in its basin.