Rice prices jumped 30 per cent to an all-time high on Thursday, raising fears of fresh outbreaks of social unrest across Asia where the grain is a staple food for more than 2.5bn people.

The increase came after Egypt, a leading exporter, imposed a formal ban on selling rice abroad to keep local prices down, and the Philippines announced plans for a major purchase of the grain in the international market to boost supplies. Global rice stocks are at their lowest since 1976.