Around 50 million chickens have been culled in an effort to prevent the spread of bird flu in Asia, according to the UN's Food and Agriculture Organisation.

"FAO estimates the number of chickens culled at around 50 million," the organisation was quoted by Agence France Presse as saying.

"Despite massive efforts to stamp out the virulent avian influenza virus, the disease continues to spread in poultry producing areas in some Asian countries," it added. 

Over the last few weeks, outbreaks of avian influenza have been reported in Cambodia, China, Indonesia, Japan, Laos, Pakistan, South Korea, Taiwan, Thailand and Vietnam.

China has said it is struggling to control the disease, which has killed 16 people in other Asian countries in recent weeks.

"Some parts of our animal disease prevention system are weak and vulnerable and the public has limited knowledge about the disease and ways to prevent it," the country's agriculture ministry was quoted by Reuters as saying.   

"It remains an arduous task for China to prevent and control the disease," it said, adding that the government was confident in its battle against the disease.

Suspected or confirmed outbreaks of bird flu have been reported in twelve of China's 31 provinces, and more than 1.2 million chickens have been culled.

Meanwhile in Thailand, the poultry industry is struggling to cope with the drop in demand for chicken products caused by the outbreak of bird flu.

"We are facing something unprecedented," Sarasin Viraphol, chief executive of Charoen Pokphand, said. Charoen Pokphand is the parent company of major Thai chicken exporter CP Foods.

Sarasin said it would take at least six months for the industry to recover, reported Dow Jones. Two of Thailand's major poultry buyers, the EU and Japan, have banned imports of raw Thai poultry products.