The disease, known as inflammatory palmoplantar hyperkeratosis syndrome, causes swelling and lesions in the hands, feet and liver, the World Health Organisation and Ministry of Health said in a joint statement.

It has only been found in Ba To district in Quang Ngai province and is not likely to be contagious, they said.

Investigations into the cause of the disease have revealed few clues, but there is no evidence of heavy metals or agrochemicals, both common causes of poisoning.

The disease first appeared in April 2011 but only recently received widespread coverage in the local press.

To protect residents, the Health Ministry has provided rice and vitamin supplements to people in the district as well as sanitation services.

The ministry called in the WHO in early June to help contain the outbreak, but this is their first official joint statement.

"As we do not know what causes the syndrome, or its source of transmission, identifying the cause may take longer than anticipated or prove elusive," WHO country director Takeshi Kasai said. (DPA)