The new bird flu virus that ha killed six people in more areas in Shanghai has led Chinese authorities to slaughter over 20,000 birds at a large poultry market in the city, according to reports.

News of the outbreak dominated China's main Internet portals. There were photographs of workers in white coveralls carrying out the culling in Shanghai and recommendations that people take banlangen, a popular herbal cold remedy. Anxious residents have been crowding emergency rooms at the first sign of respiratory problems. And at a KFC restaurant in Beijing, employees stood idle as mounds of fried chicken went largely unsold.

The new strain of bird flu has infected 16 people in China, all in the east of the country. Six people have died, and the outbreak has spread concern overseas and sparked a sell-off in airline shares in Europe and Hong Kong.

"It was the Ministry of Health and Family Planning that first came to us and volunteered the information," said Gregory Hartl, a spokesman for the World Health Organization in Geneva. "Their response has been excellent."

Experts say the virus appears to respond to existing influenza medications like Tamiflu and Relenza. In the United States, federal health officials on Thursday said they had begun working on a vaccine for H7N9.