Two major US bulk retailers are rationing the sale of large bags of rice to consumers amid a growing global food crisis marked by skyrocketing prices and heavy pressure on demand.

Sam's Club, a chain owned by retail giant Wal-Mart, announced today it was placing a limit of four 20-pound (9kgs)  bags per person for imported jasmine, basmati and long grain white rices as a precautionary step.

Sam's Club said the temporary cap is intended to ensure there is plenty of rice for all its members, which has 600 stores across the United States.

The move follows similar steps taken by its main rival, Costco,  which has also limited the sale of rice in its stores.

Both companies insist that they have plenty of rice but say the  steps were necessary to ensure there was enough for all of their  clients.

The measure appears aimed at preventing over-stocking among  customers concerned by the surging prices of commodities worldwide.

Small restaurants and businesses fill their freezers and pantries with products from big-box retailers such as Sam's Club and  Costco.

David Coia of the USA Rice Federation said there is no rice shortage in the US.

He predicted that pressure on the price of rice would ease by the end of next year, noting that more and more fields are being  used to grow rice.

US rice production provides 88% of the domestic consumption while imports from countries such as Thailand and Vietnam make up the rest.

The rationing steps came as the price of rice has surged worldwide due to the rising costs of energy and fertilizers,  droughts in some rice producing countries and higher demand.

Some countries have taken drastic steps such as limiting or  suspending rice exports to ensure they meet domestic demand.

The price of certain types of rice rose by 50% in recent months, causing tension in the poorest parts of the world.

The high price of rice sparked violent protests in Haiti earlier this month, forcing the government to issue an order to lower prices.

In the Philippines, the army distributed rice in impoverished neighbourhoods to prevent tension.

The World Bank warned this month that the higher food prices  could push 100 million people in poorer developing countries further into poverty

Wal-Mart owns British supermarket chain Asda and fears are growing that rice rationing could now be introduced in the UK.

Rice is already being rationed by shopkeepers in Asian neighbourhoods in the UK to prevent hoarding.

Yesterday the price of rice hit an all-time high per hundred pound weight of $24.74. It has gone up by 68% this year.

The EU has called on India and Vietnam, the world's biggest producers, to reverse a decision they have made to ban rice exports.

China and Egypt have also banned exports.