Chinese health officials said Saturday that a man has tested positive for the deadly H5N1 bird flu virus in the Chinese city of Shenzhen.

The southern city borders Hong Kong, where thousands of chickens were slaughtered and live poultry imports from China were suspended after two birds tested positive with the strain earlier this month.

Officials in Shenzhen say the 39-year-old bus driver, surnamed Chen, was hospitalized with a fever on December 21 and tested positive for the virus. He is now in critical condition and receiving emergency treatment.

The virus has killed more than 330 people around the world since it was first detected in 2003, with most human infections caused by direct contact with birds.

Scientists fear H5N1 could mutate into a form readily transmissible between humans, with the potential to cause millions of deaths.