Relatives have begun identifying victims of the weekend flooding in and around the provincial town of Dire Dawa.
Officials said 206 bodies had been recovered but the toll was expected to climb as 300 people were still unaccounted for.
"We have been able to recover 206 bodies and we have also rescued 96 injured people," said an official with Ethiopia's federal Disaster Prevention and Preparedness Commission.
"The search and rescue efforts are still going on but we expect the death toll to rise," the official said.
Earlier Prime Minister Meles Zenawi flew into Dire Dawa to inspect the damage. "It is a sad day to all of us," Mr Meles said, "We have lost our brothers and sisters."
Dire Dawa has a population of about 400,000 and is about 500 kilometres east of Addis Ababa.
Aid for victims
Federal authorities said they had started delivering humanitarian supplies to the victims.
"We have organised every support we can to provide such as shelters, food and blankets as well as medical support. We will be working on long term reconstruction and rehabilitation plan," said Simon Mechale, a top official in the country's Disaster Preparedness and Prevention Office.
"We have opened a special bank account for those who want to help" the flood victims, Mr Mechale explained.
Residents said they were using their bare hands, hoes, trowels, shovels as well as bulldozers and other earth-moving equipment to dig through sand, mud and rubble in search of bodies or people still alive.
Aid workers said about 10,000 had been left homeless by the waters from the swollen Dechatu and Dire Dawa rivers which broke their banks, sweeping through the town and nearby villages, killing many while they slept.
The floods in the Addis Ketema, Genfele, Coca Cola and Aftessa districts caused massive property damage, destroying hundreds of homes, trading stalls and cutting a key road linking the town to Addis Ababa.
The waters also brought down electricity and telephone lines, further complicating rescue efforts in an area in Ethiopia's lowlands that is prone to flooding during the June-to-September rainy season.
Last year, at least 200 people were killed and more than 260,000 displaced when heavy rains pounded the region, flooding rivers that quickly attracted large numbers of crocodiles and forced survivors to cling to trees to escape.
Ethiopia, a nation of about 70 million people, has frequently been ravaged by natural calamities, notably drought and famine.
The floods follow a devastating drought that hit the east Africa region, threatening the lives of about 15 million people in five countries, including Ethiopia and neighbouring Somalia and Kenya.