Hong Kong has ordered three million doses of swine flu vaccine -- enough for nearly half the city's population -- as it braces for more outbreaks of the virus this winter, officials said.

The health department ordered the vaccine from French drug maker Sanofi Pasteur with the first half a million doses scheduled to arrive by December. The remaining 2.5 million doses will arrive in January, the department said.

A free vaccination program next month will be offered to about two million people in high-risk groups, including healthcare workers, pregnant women, the elderly and children under six, the department said.

The program is voluntary, it added.

People in lower-risk groups can get the vaccine for a fee which has not yet been determined, a health department spokeswoman told AFP.

"More outbreaks are expected during flu season in early next year," the health department said in a statement.

Thirty-nine people have died of swine flu in Hong Kong with about 32,000 people infected, officials said.

The illness has killed more than 5,700 people worldwide since it was first uncovered in April, the World Health Organization has said.

Hong Kong is very nervous about infectious diseases following the outbreak of the SARS virus in 2003, which killed 300 people here and a further 500 around the world.