Police will release details of the investigation as soon as possible, local authorities said.

The local government has assigned 20 therapists to the school to deal with possible post-traumatic stress, said Liao Hanren, deputy head of the municipal education bureau.

Classes are scheduled to resume Wednesday, and psychological counseling will be provided, Liao said.

The latest tragedy again highlights the threat to social security posed by the lack of treatment for the mentally ill. Only one in five such patients gets professional treatment in the country, which has more than 16 million people suffering mental problems, experts estimated.

They blamed low awareness of the possible danger and widespread discrimination against the mentally ill for the situation.

A national mental health law, first drafted in the 1980s, aims to provide the mentally ill with legal protection and subsidized health care.

Once passed, patients without family support will have access to free shelter and treatment provided by the government.

Pang Yu, a doctor at Beijing Huilongguan Hospital, a leading psychiatric hospital in the country, said the legislation has been shelved because of the huge funds required.

Currently, only a few prosperous provinces and cities such as Beijing, Shanghai and Guangdong have drafted regional regulations on mental health.

Patients largely depend on families for help, financially and psychologically, Pang noted.

"Without national legislation and government funding, the problem cannot be solved," he noted.

So far legislation exists for only one disease, AIDS, for which patients have access to free treatment and drugs.

That costs the central government several billon yuan each year, official figures show.