April 18 (Bloomberg) -- Rice futures rose for a fifth day, recording the biggest weekly advance in at least seven years, on concern export curbs imposed by China and Vietnam will spread as importing nations struggle to meet their needs.

India and Egypt have curbed sales this year to safeguard local supplies. The gain in rice, as well as energy and wheat, has prompted the United Nations to warn that civil unrest may spread because the poor in Africa and Asia can't afford to eat, and their governments can't fund or find sufficient imports.

Rice prices today rose to a record for the seventh time this month, and the Chicago Board of Trade raised its daily trading limits after futures rose the most allowed twice this week. Availability of the world's most-consumed grain has decreased as countries restrict shipments in an effort to slow rising food costs and feed domestic populations.

``More and more countries will have restrictions on exports,'' Frederic Neumann, an economist at HSBC Global Research, said by phone today from Hong Kong. ``There's some pressure on the Thai government to curtail shipments.''

Rice for May delivery rose 41 cents, or 1.8 percent, to close at $23.71 per 100 pounds on the Chicago Board of Trade, after earlier reaching $24.355, the highest ever. The contract gained 13 percent for the week and has more than doubled in the past year.

Rising Demand

Demand for rice will continue to be strong, said Darrell Holaday, president of Advanced Market Concepts in Manhattan, Kansas.

``There's no substitute for rice,'' Holaday said. ``Maybe some people in Asia will eat more noodles and less rice.''

Thailand, the world's largest rice exporter, boosted shipments 66 percent in the first three months, according to Commerce Minister Mingkwan Sangsuwan on April 16. The nation's 100 percent Grade B White Rice gained 54 percent in the month to April 9, according to data from the Rice Exporters' Association.

The Philippines, the world's biggest rice importer, received offers for just two-thirds of the grain it sought at a tender yesterday at prices about 40 percent higher than in March. The country, which imported 1.9 million tons of rice last year, fills 10 percent to 15 percent of local needs from external suppliers.

Slowing Purchases

The jump in rice prices has forced some buyers to cut the size of their orders, said Apichat Chansakulporn, managing director of President Agri Trading Ltd., Thailand's fourth- largest rice exporter.

``Clients are slowing their purchases because the prices are very high,'' Apichat said by phone from Bangkok today. Price gains were ``driven more by psychological impact than real demand and supply. The perception is now toward an uptrend.''

A global food crisis has reached ``emergency proportions,'' United Nations Secretary-General Ban Ki-Moon said April 14. The World Bank has forecast that 33 nations from Mexico to Yemen may face social unrest after food and energy costs increased.

China, the world's most populous nation, has started to block or tax some food-related exports to make sure that local supplies remain adequate. The country set a tax on rice shipments at 5 percent this year and started to tax wheat exports at 20 percent.

`Control Exports'

The world's fastest-growing major economy announced yesterday that it was increasing the tax on fertilizer shipments to ``control exports'' and damp local prices, according to the Finance Ministry. China also turned down a Philippine request for wheat exports, Trade Minister Peter Favila said April 11.

Sumeth Laomoraphorn, president of C.P. Intertrade Ltd., Thailand's sixth-largest rice exporter, said the pace of purchases from some nations was beginning to slow.

``Orders from China are slowing, they may perceive that fragrant and white rice from Thailand and Vietnam is overly expensive,'' Sumeth said today. ``Some African countries are chasing prices up, but some in that region are balking at buying more because they have limited financial resources.''

The Chicago rice contract's so-called relative-strength index reached 84 earlier today, and has traded above 70 all this week. Some traders regard a reading above 70 as a signal the price may be set to drop.

Food Summit

The Philippines called this month for an Asian summit on escalating food prices, especially rice, and urged India, China, Japan and the members of the 10-state Association of Southeast Asian Nations to attend.

World leaders ``must come together and identify the issues, including rising fuel prices and rising demand,'' Al-Ghazim Wurie, the World Food Program's country director for the Philippines, said in an interview today. After collective steps to increase output, ``we'll begin to see a downward trend in prices.''

Households in poorer countries spend a larger share of their income on food compared with those in richer nations, magnifying the impact of costlier rice, wheat and meat, according to the U.S. Department of Agriculture.

An average household in India spent 32 percent of its income on food last year compared with 6 percent for a household in the U.S., data from the department show. The figure for Indonesia was 43 percent, and 36 percent for the Philippines.

``Poorer countries tend to suffer more than developed countries,'' HSBC's Neumann said. ``It is the poor who shoulder the biggest burden.''

To contact the reporters on this story: Rattaphol Onsanit in Bangkok at ronsanit@bloomberg.net; Luzi Ann Javier in Manila at ljavier@bloomberg.net

Last Updated: April 18, 2008 15:00 EDT