Chinese authorities have begun slaughtering birds at a poultry market in Shanghai as the death toll from a new strain of bird flu mounted to six.
State news agency Xinhua said the Huhuai market for live birds in Shanghai had been shut down and birds were being culled after authorities detected the H7N9 virus from samples of pigeons in the market.
All of the 14 reported infections from the H7N9 bird flu strain have been in eastern China and at least four of the dead are in Shanghai.
Xinhua did not say how many birds would be culled.
The strain does not appear to be transmitted from human to human, but Hong Kong airport authorities said they were taking precautions. Vietnam banned imports of Chinese poultry.
In Japan, airports have put up posters at entry points warning all passengers from China to seek medical attention if they have flu-like symptoms.
In the US, the White House said it was monitoring the situation and the Centers for Disease Control and Prevention said it had started work on a vaccine if it was needed.
It would take five to six months to begin commercial production.
With the fear that a SARS-like epidemic could re-emerge, China said it was pulling out the stops to combat the virus.
In 2003, Chinese authorities initially tried to cover up an epidemic of Severe Acute Respiratory Syndrome (SARS), which emerged in China and killed about 10% of the 8,000 people it infected worldwide.
Sanofi Pasteur, the world's largest flu vaccine manufacturer, said it was in continuous contact with the WHO through the International Federation of Pharmaceutical Manufacturers and Associations, but it was too soon to know the significance of the Chinese cases.
Preliminary test results suggest the new flu strain responds to treatment with Roche's drug Tamiflu and GSK's Relenza, according to the WHO.
Other strains of bird flu, such as H5N1, have been circulating for many years and can be transmitted from bird to bird, and bird to human, but not generally from human to human.