Ethiopia's government has warned it will run out of emergency food aid next month as the number of drought victims in the East African country reached 7.8 million.
The country's disaster relief chief Mitiku Kassa said it needs more than one billion dollars (£784 million) for emergency food assistance.
Seasonal rains have been critically small and local cattle are dying.
The number of drought victims has risen by two million people in the past four months.
An international delegation visited one of the worst-affected areas on Friday near the border with Somalia, which suffers from widespread drought as well.
The International Organisation for Migration said hundreds of thousands of people have been displaced, with the problem compounded as people pour into Ethiopia from Somalia.
A United Nations humanitarian envoy said donor fatigue and similar crises elsewhere have hurt aid efforts.
Both Somalia and neighbouring South Sudan are among four countries recently singled out by the United Nations in a 4.4 billion dollar (£3.4 billion) aid appeal to avert catastrophic hunger and famine.
Famine has already been declared for two counties in South Sudan.
"Our main concern should be for this drought in Ethiopia not to degenerate into a famine," said the humanitarian envoy, Ahmed Al- Meraikhi.
The UN has warned that Ethiopia's drought will pose a severe challenge to the humanitarian community by mid-July with the current slow pace of aid.
Along with the drought, Ethiopia also faces an outbreak of what authorities call acute watery diarrhoea, though critics have said the government should call it cholera instead.
"I've never seen the resources so poor to respond to the crisis," the country director for aid group Save the Children, John Graham, said of the drought.
"It is very worrying. These people are not going to be able to continue to survive in these dilapidated displaced people's camps.
"It could get very much worse. We are also worried that some of the children affected by the drought may die."