Farmers in western Kenya are defying an order to sell their maize to the government to ease hunger elsewhere.
Aid agencies say water sources are drying up
Much of East Africa is currently suffering a severe drought.
But western Kenya has enjoyed a bumper harvest, prompting the government to order all farmers there to sell their stocks in exchange for credit notes.
Kenyan Finance Minister David Mwiraria has warned that the government may soon have to cut its funding to ministries to cover the costs of the drought.
Kenya: 2.5m people
The BBC's Muliro Telewa in Kisumu says Tanzanian businessmen have been buying the maize in bulk and exporting it to Malawi and Zambia, which are also experiencing food shortages due to drought.
Our correspondent says the businessmen sell the maize to international aid agencies and pay cash to the farmers, whereas the Kenyan government is only offering them credit notes.
Earlier this month the government said it would put aside $14m to purchase the maize.
Mr Mwiraria said that water shortages in the country's lakes and rivers had caused a reduction in hydro-electric power, pushing up the cost of energy.
The minister said that if donor funding from abroad was not received, he would be forced to make budget changes.
Health Minister Charity Ngilu said her department could not cope with cuts to the health budget.
"I am urging Mr Mwiraria to instead increase the health budget because I believe that more people will visit health centres and hospitals frequently because of diseases related to famine and drought," Kenya's Daily Nation newspaper quotes Ms Ngilu as saying.
Kenyan has appealed for $150m to save the lives of people threatened by famine.
Kenya says its main priority is to feed the 2.5 million people at immediate risk, almost 10% of the population.
The United Nations World Food Programme has warned that 11 million people across the Horn of Africa need food aid.