Emergency workers struggled to reach seven villages hit by raging flood waters from the Omo River and its tributaries in the country's south while forecasters warned of more downpours.
"The death toll from the Omo River disaster has now reached 194," state-run Ethiopian television reported, citing police reports that said almost 3,000 head of livestock had been swept away.
The new toll was a sharp increase from the 135 reported earlier in the day by officials.
Villages submerged
They warned that the number of fatalities was likely to rise in the second deadly flash flooding incident to hit Ethiopia this month.
"There are seven villages surrounded by water and unreachable by helicopter," regional governor Shiferaw Shegute said.
Mr Shegute said that poor weather had prevented helicopters from landing and forced officials to send boats to the area.
South Omo police commissioner Tsegay Muluneh said the affected villages were submerged and surrounded by water, leaving residents without shelter and sleeping in the open.
The villages are located about 700 kilometres from the Ethiopian capital Addis Ababa.
"As many of their houses are submerged, they seem to have spent the night in the open air," he said.
While frantic efforts continued to save those stranded, meteorologists warned of more heavy rains blamed for flash floods that killed 256 people in eastern Ethiopia last week.
Relief efforts
Ethiopia's National Meteorological Agency (NMA) said six areas in the north, west and south would likely be affected by unusually heavy rains before the end of the month.
They are - West Tigray, Amhara, Benishangule Gumuz, Central and Western Oromia and Addis Ababa.
The latest deaths bring the toll to at least 450 drowned by flooding in Ethiopia in less than two weeks as the rainy season which lasts to September takes hold.
The United Nations, which has started distributing 170 tonnes of relief supplies and non-food items, called for a speedy response to avoid catastrophe around Dire Dawa in the Ethiopian lowlands.
Ethiopia, home to some 70 million people, has suffered heavy floods and droughts in recent years.
In the past few years, flooding has affected large areas of eastern and southern Ethiopia, displacing tens of thousands of people and causing damage running into millions of dollars.