HONG KONG - Chinese officials have confirmed that bird flu was to blame for killing chickens in poultry markets in the southern Chinese city of Guangzhou, Hong Kong´s health bureau Sunday.

China´s Ministry of Agriculture notified the administration that the birds tested positive for the H5N1 bird flu virus, marking the country´s fifth outbreak among poultry this year, Hong Kong´s Food and Health Bureau said in a statement.

The Ministry of Agriculture also said on its Web site that last week´s outbreak in Guangzhou killed 114 birds and resulted in the slaughter of 518 others. But it has been contained, the ministry said.

China, which raises more poultry than any other country worldwide, has vowed to aggressively fight the virus. H5N1 has killed at least 235 people worldwide, according to the World Health Organization. Scientists fear it could mutate into a form that spreads easily among humans, potentially sparking a pandemic that kills millions. So far, most human cases have been linked to contact with infected birds.

China has already reported three human bird flu deaths this year, including a 44-year-old migrant worker last month in southern Guangdong province. It has recorded 20 human deaths since the virus began ravaging Asian poultry stocks in late 2003.