China is now in process of sharing more human avian flu virus samples with the World Health organization, a senior Chinese health official said in Beijing yesterday.

China will provide four samples of human bird flu virus to WHO,which will be the second time that China has offered the human virus isolation, according to Wang Yu, director of the Chinese Center for Disease Control and Prevention (CDC).

"The handover is still in process," Wang said on the sidelines of an ongoing health conference in Beijing.

China forwarded two bird flu virus samples along with relevant virus information to WHO last December.

Dr. Shigeru Omi, WHO western Pacific regional director said earlier that it is a major contribution made by China to the global fight against the epidemic to share avian flu virus samples and information with the WHO.

Wang said that current lab tests of the human cases in China show that there have not been mutations in the H5N1 strains of avian flu virus.

But, he stressed, the recent human cases in Guangzhou and Shanghai have posed a bigger challenge for China, because it was believed that all the previous cases in rural China occurred due to low level of health conditions and small hospitals there.

Wang said that the two cases show that even in big cities with better health conditions and easier access to hospitals, cases still occur.

"Although there's no evidence that the two patients had clear exposure to dead poultry, it doesn't mean there's no virus in poultry in the city environment," said Wenqing Zhang, with the WHO's global influenza programme.

She said that national pandemic preparedness is key to reduce death and social and economic disruption for a possible bird flu pandemic, although the severity and timing is unknown.

Up till now, China has reported 16 human cases and 11 deaths from the virulent H5N1 strain of bird flu.