Food, water, health care and other non-food items are needed to help the inhabitants of the Somali and Oromiya administrative regions of Ethiopia, the UN Office for the Coordination of Humanitarian Affairs (OCHA) reported. The Southern Nations, Nationalities and People's Region (SNNPR) is also affected.
A multi-agency UN mission is being dispatched to the affected area to identify the biggest emergency and recovery needs, according to OCHA.
The UN World Health Organization (WHO) is also finalizing preparations to send emergency health kits after discussions with national health authorities.
The floods, which have occurred in an area beset by drought in recent months, follow heavy rains in both the Somali region and the highlands of the neighbouring Oromiya region. The rains caused the Wabi Shebelle, Genale, Woito and Omo rivers to break their banks.
Large swathes of Ethiopia remain hard-hit by persistent drought, and OCHA has warned that millions of dollars are needed to protect the country's poorest from malnutrition, starvation and disease.