HONG KONG  The United Nations’ food agency issued an alert on Tuesday warning that a severe drought was threatening the wheat crop in China, the world’s largest wheat producer, and resulting in shortages of drinking water for people and livestock.

China has been essentially self-sufficient in grain for decades, for national security reasons. Any move by China to import large quantities of food in response to the drought could drive international prices even higher than the record levels recently reached.

“China’s grain situation is critical to the rest of the world  if they are forced to go out on the market to procure adequate supplies for their population, it could send huge shock waves through the world’s grain markets,” said Robert S. Zeigler, the director general of the International Rice Research Institute in Los Baños, in the Philippines.

The state-run news media in China warned Monday that the country’s major agricultural regions were facing their worst drought in 60 years. On Tuesday the state news agency Xinhua said that Shandong Province, a cornerstone of Chinese grain production, was bracing for its worst drought in 200 years unless substantial precipitation came by the end of this month.