BEIJING -- A Chinese vaccine developer announced on Tuesday it will expand production facilities to produce massive quantities of human bird flu vaccine once the drug passes two more rounds of clinical trials.

After the expansion, which is expected to take six months, the company will increase its annual production from 8 million vaccines to 20 million, according to Beijing Sinovac Biotech Co., a Beijing-based pharmaceutical company. The company developed the human bird flu vaccine together with China's Ministry of Science and Technology, and China Disease Control and Prevention Center.

Preliminary clinical tests have shown that the vaccine is safe and effective for human use, researchers said.

"These results indicate that we should expand our production capabilities to prepare for mass production of the vaccine against a possible bird flu pandemic," the company's spokesman said.

Results from the first-phase trails, which ended in June, showed the 120 people who were vaccinated had no serious adverse reactions.

In China, a vaccine is allowed to enter the market after it completes three phases of clinical trials.

Bird flu remains essentially an animal disease, but experts fear that the H5N1 virus could mutate into a form that could pass easily among humans.

Worldwide, about a dozen companies are conducting clinical trials on bird flu vaccines.

According to the World Health Organization, the H5N1 virus has proven difficult to predict, and as drug companies move forward with their pandemic vaccine development, they may be gambling on which virus they think is most likely to mutate into a killer strain.

The virus has killed 14 people in China since 2003 and 21 Chinese have contracted the virus.

The latest case involved a 62-year-old man in Xinjiang Uygur Autonomous Region, who died on July 12.