Chinese authorities have vowed zero tolerance and harsh punishments for illegal sales and growing of genetically modified (GM) crops days after media exposure of GM rice on sale at a supermarket in central China.

"The ministry will punish any companies or individuals who illegally grow or sell GM grains, and there will be no tolerance for these practices," said a statement sent to Xinhua on Tuesday by the office in charge of GM food safety with the Ministry of Agriculture (MOA).

China Central Television (CCTV) found GM rice, which is illegal to sell or grow commercially in China, on sale in a supermarket in Wuhan, capital city of central Hubei Province, the broadcaster reported on Saturday.

CCTV commissioned tests on five packs of rice picked at random from the supermarket's shelves. Three were found to contain a GM variety.

CCTV also found evidence that GM rice was being sold in neighboring Hunan, Anhui and Fujian provinces.

While working to develop modern biotechnology, China has taken a wary approach to GM crops, fearing possible risks.

It has allowed several GM crops to be grown, including cotton, peppers, tomatoes and papayas, and has authorized imports of GM soybeans and corn.

However, it does not allow commercial production or sale of GM grains, including rice, although the authorities have approved the experimental planting of two strains of pest-resisted GM rice.

The safety certificates issued for this experimental planting in 2009 expire this year, and commercial production is yet to be started.

Authorities have stressed that this approval of experimentation does not equate to a broader official favoring of GM grains.

"The granting of safety certificates for GM food is not equal to allowing commercial production," Tuesday's statement quoted an anonymous official as saying.

Approval is needed for GM crops, be it production of seeds, testing or growing, the official added.

The ministry has ordered all provincial agricultural authorities to strengthen oversight and fight illegal production and sale of seeds for GM crops, according to the statement.

Chen Xiaohua, deputy minister of the MOA, said earlier this year that China would continue to take an "active and cautious" policy toward GM crops and had set no timetable on the commercial production of GM products.

GM scandal hits China's rice sales

A central Chinese city has reported reduced rice sales since a supermarket was exposed selling illegal genetically modified (GM) rice.

Sales staff at several supermarkets in Wuhan, capital of Hubei, said rice sales dropped suddenly this week following a China Central Television report on Saturday that accused a local supermarket of selling rice that contained GM varieties.

"Customers keep asking whether it is GM rice," said one saleswoman at Zhongbai, a local supermarket chain.

China has not approved commercial planting or sales of GM rice and the Ministry of Agriculture on Tuesday promised zero tolerance for sales and cultivation of GM crops.

Hubei has launched an investigation following the media exposure.

Though many scientists have defended the safety of GM technology, sales remain controversial in China, with many consumers complaining of not being well enough informed.

"I'm not against GM products, but being kept in the dark. You should let consumers decide whether to eat GM products," said a shopper surnamed Wang.