Chinese food safety officials are investigating reports that hormone-tainted milk powder has caused baby girls to show signs of premature sexual development, a Health Ministry spokesman said on Tuesday.

Deng Haihua said his ministry took consumer concerns seriously and had already arranged for officials to start tests on samples of powder and launch an investigation into what had caused the infants to show symptoms of breast development.

"They have also organised for medical experts to carry out clinical tests on the affected girls, and do a medical investigation, to analyse the cause of the girls' illness," he told journalists at a regular scheduled news conference.   

Shares of Chinese baby-formula maker Synutra International fell as much as 35 percent on Monday after Chinese media linked it to allegations of abnormal development in baby girls.

In a statement late on Monday, the company denied the reports and said it was in the process of taking legal action to protect its brand.

"We have worked closely with state authorities, including the Chinese Dairy Association and the office of food safety, to test product samples, to prove that these claims are false. We expect that the results of these tests should be made public soon," Synutra Chief Executive Liang Zhang said.

Several state-owned Chinese newspapers, including Global Times and China Daily, reported this week that three infant girls in southern Hubei province were found with symptoms of breast development, quoting an article in the Health Times.

Synutra, which sells its products in China, said it does not add hormones to its products as suggested in the media reports and has invested heavily in research, quality control, formulations and ingredients.

Even if the claims prove unfounded, the concerns about exposure to tainted milk products has underscored the persistence of food safety problems that have alarmed consumers, undermined China's global image and sparked criminal cases.

Two years ago, at least six children died and nearly 300,000 became ill from drinking powdered milk laced with melamine, an industrial compound added to fool inspectors by giving misleadingly high results in protein tests.   

Melamine can cause kidney stones, and is used to make plastics, fertilisers and concrete. Its high nitrogen content allows protein levels to appear higher when added to milk or animal feed, allowing traders to disguise substandard products. - Reuters