Rice prices rose more than 10 per cent yesterday to a record high as African countries joined south-east Asian importers in the race to head off social unrest by securing supplies from the handful of exporters still selling the grain in the international market.

The rise in prices - 50 per cent in two weeks - threatens upheaval and has resulted in riots and soldiers overseeing supplies in some emerging countries in which the grain is a staple food.

The increase also risks stoking further inflation in emerging countries, which have been suffering the impact of record oil prices and the rise in price of other agricultural commodities - including wheat, maize and vegetable oil - in the past year.

Kamal Nath, India's trade minister, said the government would crack down on hoarding of essential commodities to keep a lid on food prices. "We will not hesitate to take the strongest possible measures, including using some of the legal provisions that we have against hoarding,'' he said yesterday.

Thai medium-quality rice, a global benchmark, traded at about $850 a tonne yesterday, up from $760 a tonne last week, while the price of less representative top-quality aromatic rice broke the $1,000-a-tonne level for the first time, traders said. They added that the grain was being sold to African destinations.

In Chicago, US rice futures hit a record high of $20.45 per 100 pounds.

Although only a small amount of the grain is traded internationally, the rise in Thai prices signals the trend for the global market and also for domestic prices in countries where local production is enough to meet demand.

The price jump came as leading exporting countries, including Vietnam, India, China and Egypt, banned foreign sales. Hanoi extended its ban for two extra months until June.

Food aid officials said consumption could rise further because record food prices were forcing families to move from a diversified diet to just one staple.

Farmers delaying their harvest and middlemen hoarding stocks were also contributing to the crisis, said governments and traders.

In past weeks, traders and diplomats warned that many west African countries, where rice is a staple, had yet to purchase the grain this year, leaving them subject to record prices now.

Cries of the hungry, Page 13 www.ft.com/foodprices