An 11-year-old Cambodian boy has died of bird flu, a hospital official said Monday, the impoverished kingdom's third confirmed fatality -- all children -- from the illness this year.

The boy, who was from northern Kampong Chhnang province, died on Friday morning six hours after he was admitted to hospital, according to Denis Laurent, deputy director of Kantha Bopha Hospital in the capital.

"We tried to do our best... but it was too late and we could not do anything to save him," he told AFP.

Another doctor said the boy had eaten infected poultry.

In an unrelated case, a second boy -- aged eight-years-old -- is in a stable condition in hospital in Phnom Penh after testing positive for the H5N1 deadly flu.

The disease typically spreads from birds to humans through direct contact. But experts fear it could mutate into a form easily transmissible between humans, with the potential to trigger a pandemic.

Authorities have struggled to control bird flu outbreaks in Cambodia, which recorded 14 deaths from the illness last year, the deadliest outbreak of the virus in the country since 2003.

Cambodian children are at particular risk as they often live in close proximity to poultry.

At the start of the month, a three-year-old boy from the outskirts of Phnom Penh died of H5N1.

His death came weeks after that of another eight-year-old boy, from eastern Kratie province. His two-year-old sister died the same day but authorities said tests could not be carried out to confirm she had the virus.

H5N1 has killed hundreds of people worldwide since a major outbreak in 2003, according to the WHO. Vietnam has also recorded two deaths in 2014.