A Chinese-developed vaccine against the H5N1 strain of bird flu in humans has been found safe in the first round of tests, a government news agency reported Monday.

Researchers began work on the vaccine last year, and the government said it was ready to start mass production. But any vaccine would face more tests before it could be approved for human use.

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Tests were conducted on six human volunteers at a Beijing hospital between November and June, the official Xinhua News Agency said.

Researchers said the vaccine "proved initially safe and effective," the official Xinhua News Agency reported. It gave no other details of the results, or of any plans for more testing.

The tests were conducted by the China Center for Disease Control and Prevent and a Chinese drug company, Beijing Sinovac Biotech Co., according to Xinhua.

Chinese authorities say the vaccine is meant for high-risk groups such as poultry workers.

The U.S. National Institute of Allergy and Infectious Diseases is also conducting trials on an H5N1 vaccine for humans.

China has suffered 14 human deaths from the H5N1 strain of flu — the latest a farmer who died July 12 — and dozens of outbreaks among its vast poultry flocks.

Experts fear the virus could mutate into a new strain that could spread easily from human to human, potentially causing a global pandemic.