The World Health Organisation has confirmed that a 13-year-old boy has died in Vietnam of avian influenza, or bird 'flu.
An eight-year-old girl is in a critical condition with the same disease, which has been sweeping through south-east Asia.
The virus has killed four other children and one adult, all of them in Vietnam.
Experts do not know why children have been the worst affected.
Thailand will host a meeting on Wednesday of senior health and agriculture officials from Asian countries fighting the outbreak.
Health experts fear the virus could set off an epidemic worse than SARS, another disease that crossed from animals to humans and frightened the world last year.
Vietnam, Japan, Cambodia and South Korea - all countries that have reported outbreaks - will attend the January 28 meeting in Bangkok, as will China.
Hong Kong, Singapore and the European Union, which have banned imports of Thai chicken, will send officials as well.