In an “unforeseen and unprecedented” shift, the world food supply is dwindling rapidly and food prices are soaring to historic levels, the top food and agriculture official of the United Nations warned Monday.

The changes created “a very serious risk that fewer people will be able to get food,” particularly in the developing world, said Jacques Diouf, head of the UN Food and Agriculture Organization.

The agency’s food price index rose by more than 40 percent this year, compared with 9 percent the year before - a rate that was already unacceptable, he said. New figures show that the total cost of foodstuffs imported by the neediest countries rose 25 percent, to $107 million, in the last year.