Thousands of people desperately in need of food and shelter are stranded in remote regions of the country that have been cut off by the severe flooding.
In the south, where the Omo river burst its banks on Sunday the situation is critical, state TV reported. At least 194 bodies have been recovered and 6,000 people need urgent help.
"Two army helicopters and 14 motorboats have been deployed to evacuate up to 6,000 people marooned by the floods," it said. "Bad weather has been hampering rescuers."
The heavy rains follow a period of prolonged drought.
The Dechatu river in the east burst its banks last week killing 254 people; another 250 are missing and feared dead.
Death toll could rise
Officials and aid workers have said that the toll could increase significantly due to difficulties reaching the worst affected regions.
There are fears a third river, the Awash, could soon burst its banks. About 7,000 people living near to the river are being evacuated.
Heavy rains in the the highland regions between June and August frequebtly cause floods in lowland areas of Ethiopia.
Aid workers have said that the situation has been made worse by land cultivation, deforestation and overgrazing in recent years.
Paulette Jones, spokeswoman for the World Food Programme (WFP), said: "The rivers in Ethiopia have less capacity to hold as much water as they did years before, because they are being filled up with silt.
"It takes less intensity of rainfall ... to make a river in any particular part of the country overflow."