HANGZHOU, Jan. 9 -- At least 17 children in a private kindergarten in east china's Hangzhou City have developed an unexplained condition under which their fingernails have fallen off, according to the school and local health departments.

Li Yuefang, head of the Wenshou Kindergarten, said on Thursday that the 17 kids began to experience the nail problems in December.

"No cause has been found," Li said, admitting that 12 students had been withdrawn from the kindergarten as their parents worried about their safety.

A post exposing the case appeared in an internet forum on Tuesday, saying over 50 children in the kindergarten have shown similar symptoms of separated nails.

The educational bureau in Xiacheng District of Hangzhou, which administrates the kindergarten, confirmed on Thursday that medical experts have ruled out the possibilities indoor environmental pollution and fungal infection.

The municipal center of disease control has entrusted a local air testing center to check the air quality in the kindergarten's classroom. All indicators have proved on par with relevant safety standards.

The Hangzhou No. 5 Hospital has also ruled out the possibility of fungal infection for five of the 17 kids whose symptoms are more severe than others.

Zhan Jianying, a doctor with the Zhejiang Provincial Children's Hospital, said a lack of certain microelements necessary for human bodies might be the cause.

The Xiacheng district education bureau said it will invite more experts to look into the case, and make sure kindergartens will be consistent in disinfection.