China is able to mass-produce bird flu vaccines for people, a top Chinese scientist said on Sunday.

Zhong Nanshan, an academic at the Chinese Academy of Engineering and director of the Guangzhou Institute of Respiratory Diseases, made the remark at a Guangdong provincial government news conference.

"Once the H7N9 bird flu virus begins to infect many more people, is found spreading among humans, China will mass-produce the vaccine to help halt the virus' spread," he said. "China now has the ability since researchers have developed a vaccine virus strain of H7N9 avian influenza virus."

The vaccine was jointly developed by several institutions, including the First Affiliated Hospital to Zhejiang University's School of Medicine, Hong Kong University, the Chinese Center for Disease Control and Prevention, National Institute for Food and Drug Control and the Chinese Academy of Medical Sciences.

Shu Yuelong, director of the Chinese National Influenza Center, said it was the first domestically produced influenza vaccine virus strain.

"China could share the vaccine strain with other countries through the World Health Organization to aid in H7N9 epidemic control across the world," he said.

The virus, which infects birds and people, has reportedly sickened more than 140 people in China, killing 45 since March, according to the National Health and Family Planning Commission.

Birds infected with the virus show no symptoms, experts said.

No mutations of the virus have been detected, and people have contracted the H7N9 bird flu solely by contact with birds, said Feng Zijian, director of the health emergency center of the Chinese Center for Disease Control and Prevention.

But flu strains can quickly genetically mutate to possibly become transmissible from person to person, raising the risk of a pandemic, according to the WHO.

"Even in the case of major outbreaks among people, clinical issues like immunization schedules and the primary targets still need more research and assessment," Feng said.

As the H7N9 virus is circulating among birds, humans are also at risk of contracting it, especially during the peak flu season, through winter to early spring.

Zeng Guang, chief epidemiologist at the CDC, said, "Frequent smog in winter will worsen the situation because good ventilation indoors is not possible on heavily polluted days."

Health authorities have urged health departments to make H7N9 prevention and control a priority and beef up surveillance and medical treatment for patients.

Anti-flu medications such as Tamiflu should be used on patients who show typical flu symptoms, including fever, Zhong Nanshan said.

Zhong also urged the public to maintain good hygiene and stay away from live poultry.

The first human clinical trials of experimental vaccines against H7N9, which use the new technology capable of quickly producing millions of doses, have stimulated the development of protective antibodies in most recipients, according to Swiss drug maker Novartis and Novavax, a biotech company in the United States.