The Chinese shipments resumed Thursday morning only hours before Secretary of State Hillary Rodham Clinton raised the embargo issue at a news conference in Honolulu, where she announced plans to visit China on Saturday to pursue the matter with Chinese officials.

Mrs. Clinton spoke after meeting with Japan’s foreign minister, Seiji Maehara, and said that the suspension of shipments had been a “wake-up call” and that both countries would have to find alternative sources of rare earth materials.

Because China is on the opposite side of the international dateline from Honolulu, it was already midday on Thursday in China by the time Mrs. Clinton spoke in Honolulu on Wednesday. Later, after the New York Times Web site reported that the embargo had been lifted, an administration official said the United States was still seeking clarification from China.

In recent weeks, senior Chinese commerce ministry officials have insisted that they had not issued any regulations halting shipments. They have suggested at various times  implausibly, in the view of industry executives  that the halt resulted from a spontaneous and simultaneous decision by the country’s 32 authorized rare earth exporters not to make shipments, whether because of a deterioration in Sino-Japanese relations or a greater thoroughness on the part of customs inspectors.

Image Credit... The New York Times

Under this year’s quota  30,300 metric tons of authorized shipments  only a few thousand metric tons remain to be exported in 2010. Meanwhile, annual demand outside China for raw rare earths approaches 50,000 tons, according to industry estimates.

The Chinese government assigns its quotas to the authorized exporters, who often trade those rights like commodities. As recently as 2008, the quota rights themselves had no market value. But lately, with rising demand, the value of the remaining quotas has soared to the point that the right to export a single ton of rare earths from China now sells for about $40,000, including special Chinese taxes.