Rice prices rose more than 10 per cent to record levels yesterday 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 for about 3bn people.