The WFP says some farmers have been hit by "almost total crop loss"
The United Nations food agency will give food aid to more than double the number of people it is currently helping in Kenya.
The World Food Programme (WFP) will now feed 3.5 million people hit by drought and high food prices.
Many families are struggling to find food for one meal a day, it said.
The Kenyan government declared a national disaster in January following the failure of the short rains in south-eastern and coastal areas.
BBC correspondents say last year's political violence has also contributed to food shortages because many displaced people were unable to plant their crops.
Falling remittances from abroad, due to the global financial crisis, have compounded the crisis, the WFP said.
"Kenyans already struggling with drought and high food prices are now being hit by the financial crisis," said Burkard Oberle, WFP Kenya country director.
He added that rates of child malnutrition in pastoral and marginal agricultural districts, for instance, were already beginning to reach or surpass crisis levels.
In response, the WFP will increase the numbers of people in Kenya receiving general food distributions from 1.2 million people to 2.5 million in the period until February 2010.
A drought in Kenya in 2006 left many animals dead
It also said it will provide 1.5 million children with school meals as an incentive to keep them in education.
Subsistence farmers in south-eastern and coastal areas have experienced "almost total crop loss", after the failure of October-December short rains, the WFP said.
High food prices have exacerbated the crisis. Maize prices have increased by up to 130% in parts of the country since last year.
Inflation along with high fuel and fertilizer prices have stopped farmers producing larger harvests.
The new WFP operation in Kenya will cost a total of $474m (£340m) from April 2009 through March 2012.
The agency is appealing to donors for a total of $244m (£175m) dollars to prevent the most vulnerable from going hungry.