Officials said the number of Kenyans needing food aid to stave off starvation had shot up to 3.5 million from an earlier estimate of 2.5 million, and that additional assistance was imperative to prevent mass deaths.
"Nearly 3.5 million rural pastoralists and farmers, including 500,000 schoolchildren ... are affected and in need of emergency assistance," Kenya's Special Programs Minister John Munyes told a meeting of donors.
"A total of 396,525 metric tonnes of additional food assistance ... will be required to avoid mass suffering for the next 12 months," he said, noting the cost of that aid would be A$300 million.
Food aid depleted
Without immediate donations, stocks of food aid will be depleted by March, according to the UN World Food Programme (WFP), which added that another A$16 million dollars in non-food assistance is needed.
"The government of Kenya and its partners must act now to avoid a massive humanitarian catastrophe," it said.
At least 40 people, mainly children in northeast Kenya, have died of drought-related malnutrition and related illness since December and Kenyan President Mwai Kibaki has declared the situation a national disaster.
Tens of thousands of cattle, goats, sheep and camels have also perished, sparking tribal conflict over water and pasture and exacerbating the suffering of the livestock-dependent populations of the most-affected regions.
Kenya is one of four east African countries worst-hit by the by the drought which has seen the failure of rains in some places for five years and put around eight million people at risk of starvation across the region.
"Many Kenyans ... are already living in the edge and unless donors respond immediately, we fear the worst," said Tesema Negash, WFP country director for Kenya.
"Without fresh pledges, WFP will not be able to meet the March needs.
"The rains have failed and to save lives in the coming weeks and months ahead, it is essential that both cash and in-kind contributions of food are made today to assist with (the) emergency response."
Kenya's last food emergency occurred between March 2000 and October 2002.
At its height in 2001, some 4.4 million people required food aid.
Oxfam appeal
The British charity Oxfam said that without an immediate doubling of international assistance, Kenya would likely face its "worst humanitarian crisis" since it won independence from Britain in 1963.
"What is crystal clear is that if donors don't rapidly fund the new UN appeal, the situation which is already critical, will get much worse," it said in a statement.
Oxfam said the scale of the crisis in Kenya's worst-hit regions was now at a "critical phase" with malnutrition rates in some areas at more than 30 percent, twice the 15-percent level at which an emergency is declared.
"We can still stop this turning into full-blown crisis but only if donor governments respond quickly and generously," it said.