The parents of children in Hunan province who took part in a study allegedly involving genetically modified rice have expressed concerns over possible health hazards.
The move comes as one of the authors of the study, Yin Shi'an, denied that the project used GM food.
Yin, a researcher with the Chinese Center for Disease Control and Prevention's Nutrition and Food Safety Institute, was listed as the third author of the study in a paper published on Aug 1 in the American Journal of Clinical Nutrition.
The paper said that in 2008, 68 children in Hengyang, Hunan province, were fed golden rice - a GM variety of rice - to test if it could help children with vitamin A deficiencies. The study was led by Tufts University in the US.
However, Liang Xiaofeng, deputy director of the China CDC, said on Tuesday that the part of the research project in which Yin participated did not involve golden rice, but that the matter is still being analysed.
"Given that the study involved many partners and that it is a complicated matter, further investigation is still under way," Liang said.
On Sunday, Hu Yuming, a researcher at the Hunan CDC who is listed as the second author of the research paper, also denied the use of golden rice and added that he had not been asked by the journal to sign the paper before the publication.
In Jiangkou township, Hunan, where the study took place in 2008, parents of the children involved have expressed their concern.
"I learned about the US research paper on the Internet," said Xie Xiaohua. "I'm really scared. My daughter took part in the study and now she looks smaller than other children of the same age. I don't know if that is related to the study."
Her daughter, Liao Ke, aged 11, was one of the more than 60 children at Jiangkou Primary School who participated in the nutrition study on the transformation of carotene in vegetables to vitamin A in children's bodies.
According to Liao, she ate three meals for free each day at school under the programme when she was 7.
"I had the meals for 15 days," she said. "But I had a fever three times at the time. My parents then asked me to quit the programme."
She recalled that the programme's rice looked no different from normal rice. Golden rice is yellow.
"We also had milk and vegetables with each meal," she said, adding that the children got a blood test each week.
"We don't know why they needed to have blood tests. But we were told by teachers that the blood would be sent to the US for testing," said Liao's mother Xie.
The programme lasted only two years.
"More children were involved in the programme in 2009," Xie said.
Before the programme, Xie was asked to sign an agreement with the school but she said that it did not mention GM rice.
Andrea Grossman, a public relations officer for Tufts University's human nutrition research centre on aging, was quoted by the Beijing Youth Daily as saying that the study on golden rice was approved by authorities in both countries after an examination by ethics committees.
According to Xie, some teachers at the school also took part in the programme. They were given school bags, pencil boxes and free tours in the provincial capital of Changsha as a reward afterward, she said.
A teacher at the primary school, surnamed Chen, whose child was also involved in the programme, said that disease control and prevention experts have started investigating the case.
"Teachers were told that the rice that children had in their meals was not genetically modified. The rice and vegetables were purchased locally," said Chen, who asked to not be fully identified.
According to Chen, the school principal was replaced after the end of the programme.
"As my son participated in the programme, I am expecting a thorough investigation. We should know the truth," he said.
Xie agreed and urged authorities to perform medical checks on the children involved in the study, who were then aged 6 to 8.
However, some Chinese agriculture and food safety experts don't agree, saying that there is no need to panic.
Chen Junshi, an academic at the Chinese Academy of Engineering and a food safety expert, said that the claims that GM food is not safe have never been proved.
He said that the research in Hengyang was about child nutrition, not the safety of golden rice.
"As long as they got the informed consent from the children's parents, it's absolutely OK," Chen said.
The public and media frenzy over the issue stem from misunderstandings about GM food and its safety, he added.
Huang Dafang, a member of the biosafety committee in charge of agricultural GM organisms, which is affiliated with the Ministry of Agriculture, said that using a new generation of GM crops, such as golden rice, to achieve nutritional improvements is now a global trend.
Golden rice, he said, is expected to be approved for commercial planting in the Philippines in the next three years. And that could also benefit China, he said.
"GM crops with the function of improving nutrition are needed particularly in mountain areas in Hainan province and in Southwest China where children usually suffer from malnutrition," he said.
"As far as I know, the committee has not received any application from foreign countries to import GM crops to China for scientific research," Huang said.
Meanwhile, Han Tianfu, a researcher at the Chinese Academy of Agricultural Sciences' Institute of Crop Science, said that golden rice doesn't pose a health hazard to consumers.
Golden rice went through a series of safety assessments before getting planting approval in the US, although he said that it hasn't received market approval.
"It's also not against any law in China to bring in some golden rice for scientific research purposes," he added.
Han called for increased GM food awareness among the Chinese public.