Widespread flooding across Ethiopia is affecting more than 100,000 people, with the number of those driven from their homes topping 36,000 and rising, the United Nations said on Tuesday.

Authorities fear further flooding is imminent and the outbreak of waterborne disease likely.

"Particularly in the western part of the country, the risk of further flooding remains high," Elisabeth Byrs, spokeswoman for the U.N. Office for Coordination of Humanitarian Affairs, said in a statement.

"AWD (Acute Watery Diarrhoea) remains of serious concern ... approximately 2,000 cases have been reported in Tigray Region since mid-July," she added.

Ethiopia faces seasonal flooding between June and September, with 48,000 Ethiopians uprooted by floods last year, but this latest round has hit non-flood-prone areas, Byrs said.

"Approximately 138,000 people in Amhara, Afar, Gambella, South Nations and Nationalities Peoples state (SNNP) and Tigray are currently affected by flooding, of which 36,000 are displaced," Byrs said.

On August 30, a U.N. mission departed to the ethnically Somali Ogaden region to assess the needs of the population, including access to food, water and health services.

"To date, the government has dispatched 1,194 tonnes of food for more than 65,000 flood-affected people," Byrs said.

The United Nations estimates up to 900 Ethiopians died last year when several rivers burst their banks. Flash floods typically happen in lowland areas of the country after heavy rains drench the highlands during the rainy season.