HANOI: The World Health Organisation said on Monday it was “concerned” about an outbreak of a mysterious skin disease in central Vietnam which has killed 19 people, mostly children.

More than 170 people have fallen ill with the unidentified illness, which causes stiffness in the limbs and ulcers on victims' hands and feet that look like severe burns.

“We are concerned about this. WHO is very aware of this case,” said Wu Guogao, the organisation's chief officer in Hanoi, adding Vietnam had not asked for help with an investigation into the outbreak.

The WHO has not been given access to any official reports on the issue.

“It is difficult to say the exact cause at this stage,” he told AFP.

The disease appears to have been concentrated mainly in Ba To district in central Quang Ngai province and the WHO said it had not heard of similar outbreaks elsewhere in the country.

Local doctors said they were waiting for the results of a recent Ministry of Health probe.

“The results of the investigation (are) not yet available. Therefore, we don't know anything more concerning the disease,” said doctor Dang Thi Phuong, director of Ba To district healthcare centre.

“As far as I know, the Ministry intends to invite foreign experts to the area to help us know more,” she told AFP, adding that many of the victims were under 10 years old.

Media reports said about one in 10 of those infected had developed serious liver disorders, but said the infection does not appear to be highly contagious.