China's agriculture ministry says there is still no timetable for the commercialization of domestically developed genetically-modified strains of corn and rice, although the country is already the world's top buyer of GMO soy.

The ministry granted safety certificates for its first genetically-modified rice and corn in 2009 but has so far refused to authorize commercial production.

"For GMO products, we are taking active but cautious measures," vice agriculture minister Chen Xiaohua told reporters on Wednesday.

Imported GMO soy and corn are already used as feed for animals in China but winning acceptance for the more widespread use of GMOs is hard to accept in a country frequently hit by food scares.

Chinese scientists have criticized the ministry for not moving forward on commercialization of the technology, which has cost billions of yuan in research over the past decade. They claim China is facing a growing food gap that can only be properly addressed through the use of GMO.

"We will actively strengthen scientific research and develop new strains with our own intellectual property rights... while we will be cautious in commercialization and application to ensure safety of the products," said Chen.

Imported GMO crops also have to comply with the country's regulations and need approval before being imported, added Chen, referring to the recent rejection of around 600,000 tonnes of U.S. corn, as well as U.S. distillers grains, over the past two months.

He declined to comment on when the ministry is likely to grant approval to Syngenta AG's MIR 162, the variety at the center of the rejections.