Floods in Niger have killed 81 people since July, the UN Office for Humanitarian Affairs announced Thursday, adding cholera outbreaks have killed a further 81 people.

"The last update of the toll of the floods dating from September 11 indicates that 527,471 people have been affected by the bad weather and 81 people have lost their lives," OCHA said in a statement in Niamey.

The previous toll established by the authorities was 68 dead and 485,000 people affected in the Sahel nation in west Africa.

Thousands of homes, schools, health centres and mosques have been destroyed, along with large quantities of food supplies, according to the authorities.

The UN office also reported outbreaks of cholera, which have claimed 81 lives since the start of the year, mainly in the west of the country.

Cholera is spreading fast in at least four places, making 3,854 people sick and notably affecting the Tillaberi regions lying by the Niger river and close to the border with Mali, OCHA said.

In the provinces and in the capital, where the Niger river level is rising significantly, most of the people stricken by flooding are being housed mainly in schools, as well as mosques and public buildings.

While preparing to move flood victims to more appropriate accommodation, the government has postponed the start of the school year from October 17 until October 27.

In neighbouring Burkina Faso, heavy rains have killed 18 people and made 21,000 homeless since June. Senegal and Nigeria have also been affected by the bad weather.