According to regulations governing the administration of central grain reserves issued in 2003, China will annually rotate 20 to 30 percent of its total central grain reserves based on domestic supply and demand.

"It is very likely that the rice produced in 2007 will soon be rotated, as it will soon be past its due date," Lu said. "For instance, some may be sold to local flour mills."

In addition, since grain reserves are usually conserved for famines and other disasters, some of the rice may have already been sent to drought and flood-stricken provinces this year, he said.

The Ministry of Agriculture would not comment on the Greenpeace report on Tuesday.

In March, however, ministry officials sought to dispel these concerns, saying "there is no commercial planting of GM food crops in China now".

Contrary to these assertions, Luo said, other illegal commercial planting cases have also been recorded in a number of different provinces in recent years, such as in Hunan and Jiangxi.

In May, for example, agricultural bureau officials in Hunan province tracked down 1.5 tons of GM rice.

"The government has, apparently, not taken strict measures to crack down on the planting of GM rice," Professor Jiang Gaoming, of the Institute of Botany at the Chinese Academy of Sciences, told China Daily.

"Farmers always have no idea about whether they are planting GM rice or not," he added. "Therefore, the government has to strengthen its control of GM rice seeds from the start."