HONG KONG - A woman has been admitted to a Hong Kong hospital on suspicion of having contracted swine flu while two other people were declared free of the virus, a health official said Monday.

The woman, who had just returned from San Francisco, was undergoing tests after showing some flu-like symptoms, Thomas Tsang, controller of the Centre of Health Protection, told reporters.

"A 27-year-old woman who returned from San Francisco is undergoing tests," said Tsang. "But remember there has been no reported case of swine flu in San Francisco so far."

He added that a 77-year-old woman who had just returned from a trip to Mexico and the United States had also been examined by doctors, along with her granddaughter, who had not travelled outside Hong Kong.

Both showed some flu symptoms but were released after being given the all-clear, Tsang said.