By Muchena Zigomo

JOHANNESBURG, July 12 (Reuters) - The impoverished African kingdom of Lesotho has declared an official food crisis after bad harvests left more than 400,000 people in need of food aid, a U.N. agency said.

The United Nations' Office for the Coordination of Humanitarian Affairs (OCHA) said Lesotho's government had declared a food security emergency based on U.N. reports showing a "major food gap" affecting a fifth of the population.

"The situation is critical for those already living on the edge, struggling to cope with the combined impact of successive crop failures, poverty and HIV/AIDS," UN emergency relief coordinator John Holmes said in a statement late on Wednesday.

"The international community must respond rapidly to assist the government in averting a crisis," he said.

UNAIDS says about 270,000 people -- making up 14 percent of Lesotho's population -- are infected with HIV, giving it one of the worst AIDS crises in the world.

The food crunch was triggered by the country's worst drought in over 30 years, which OCHA said had cut the staple maize crop harvest by more than 40 percent.

Close to 328,000 tonnes of cereals are now needed to feed hungry people in the country, which only harvested a meagre 72,000 tonnes of cereals during its last harvest, down from 126,000 tonnes last year.

Sparse supplies, and reduced harvests in neighbouring South Africa, the regional supplier, have helped to push prices beyond the reach of many in Lesotho, which is one of the poorest countries in the region.

Lesotho's crisis has spurred wider calls for food aid to other parts of southern Africa. More than 5 million people in the region, including up to four million in Zimbabwe alone, are expected to need food assistance due to drought this year, the U.N. said.

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