Thousands of flood victims remain stranded in drastic circumstances in south-west Ethiopia, relief staff say.
Hundreds have died in floods across Ethiopia in the past month
The River Omo burst its banks at the weekend, causing huge floods. About 900 have died in floods in several regions of Ethiopia in the past two weeks.
Poor weather and surging currents are hampering relief operations from the Arba Minch army base in the south-west.
One helicopter pilot said he had spotted 1,000 marooned people but had been unable to land to rescue them.
"Lack of access is having a significant impact on the ability of helicopters to move... where they are able to fly, they drop floating tubes," Vincent Lelei, deputy head of mission for the UN Office for Humanitarian Affairs (OCHA) told Reuters news agency.
Yohannes Desta of the UN World Food Programme (WFP) in Awassa said that by Friday evening rescue teams working in motorboats had managed to move 1,300 people to higher ground.
"Three helicopters have been dropping food biscuits, malaria medicine and plastic sheeting to the rescued people," he told the BBC News website.
But he said thousands remained stranded and the water was continuing to rise, affecting other towns and villages.
"Kanagten town was flooded by the rising waters on Thursday, but the residents had already left," he said.
The town of Omorate, the centre of the rescue effort, was also threatened and there were frantic efforts to reinforce dykes, he said.
Other officials estimated the rains will intensify over the next two weeks.
Local Ethiopian officials are appealing for assistance, and the International Red Cross has launched a $1.4m appeal for those affected by the flooding in Ethiopia and Sudan.
The disaster co-ordinator in the Omo region, Deftalgne Tessema, told the BBC's Network Africa programme that despite help from the federal government and the UN, so far only 14 motorboats were trying to evacuate people from islands cut off by the swollen waters.
"The boats very small. We are trying our best," he said
Flooding often hits low-lying parts of Ethiopia between June and September, when heavy showers fall on dry regions.
But correspondents say the situation is much worse this year.
In the far north, thousands of people in Tigray province are battling floods along the Tekezie river.
Dire Dawa was declared a disaster zone after last week's floods
The eastern city of Dire Dawa has been declared a disaster zone.
Local and international agencies are still providing food and help to thousands of people and to communities further north along the Awash river.
There are 256 confirmed deaths from last week's flooding in the area, but some 250 people are still missing and 10,000 were displaced.
The UN's WFP distributing relief supplies there.
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