Downpours that have killed dozens in Africa, uprooted hundreds of thousands and devastated crops could continue past the end of the rainy season and hit areas that have so far escaped floods.
"Our estimates show the floods are likely to worsen or remain at the same level up to October or early November," said U.N. World Food Program official Tasema Negash.
Experts say the rising waters may hit as yet unaffected areas in the coming days, such as Uganda's central regions.
"We are calling on the international community to come to their rescue before it is too late," said Musa Ecweru, minister for disaster preparedness in Uganda, where 300,000 people have already been affected and at least nine killed.
Scores have died in more than a dozen countries often ravaged by droughts, but now inundated by torrential downpours destroying settlements and sweeping away crops and livestock — cornerstones of Africa's developing economies.
At least 90 dead so far
Across the continent, uprooted communities shelter in abandoned schools, churches and under plastic sheeting.
Schoolboys carrying books above their heads wade through flooded fields, while villagers stand on the muddy wreckage of homes searching for missing family.
Across east Africa, more than 90 people have now died from floods and the waterborne diseases that have followed — at least 63 in Ethiopia alone.
In west Africa, the U.N. humanitarian agency OCHA says floods have affected half a million people. The International Federation of the Red Cross says 87 people have been killed in the past two months, mostly in Nigeria.
But those figures are rough estimates as hailstorms, mudslides and collapsed bridges wreak havoc with relief efforts.
In Kenya, 20,000 people driven from their homes in the largely agricultural southwest left behind a wilderness of wasted crops and drowned livestock.
"These people affected depend their lives on agriculture ... the floods will have a huge economical impact in Kenya," said Elena Velilla, Medecins Sans Frontieres' head of mission.
Nations already facing difficulties
The U.N. World Food Program says it needs $29 million in Uganda to fight the crisis in a country already burdened by thousands of refugees from neighboring Congo and more than a million people living in war displacement camps in the north.
With camps for the displaced fast swelling in countries across the center of the world's poorest continent, experts say the threat of disease is mounting quickly.
"We need medicines because we expect outbreaks of diarrhea and cholera," Ben Brown, regional co-coordinator of Ghana's National Disaster Management Organization, told Reuters.
Northern Ghana has been particularly badly hit, and the authorities there have appealed for international help to feed, clothe and house tens of thousands uprooted by rising waters that have killed at least 18.
"Malaria may be expected because we have stagnant waters and mosquitoes will breed," Brown said.
Last week in neighboring Togo, where at least 20 people have died since last month, the authorities delayed the start of the new academic year for a month after 46 schools were damaged.
And in already impoverished Mali and Niger, swarms of crop-eating locusts are now feared, OCHA said.