Hong Kong - Three patients tested negative for swine flu in Hong Kong as the densely populated city of 7 million went on alert over the outbreak.

   A 77-year-old woman and her 4-year-old granddaughter were tested after the grandmother returned from a holiday in Mexico and the US with flu-type symptoms.

   A 27-year-old woman who developed flu symptoms on April 23 after returning to Hong Kong from San Francisco was admitted to hospital Sunday.

   Tests revealed she had a type of flu which was not swine flu, a spokesman for the Hong Kong Centre for Health Protection said Monday evening.

   Earlier Monday, Hong Kong chief executive Donald Tsang warned Monday of the danger of the swine flu virus spreading to the city which has seen virus deaths in the past.

   "Hong Kong is a cosmopolitan city. We do not easily close our borders, and it is quite possible people carrying this virus during the hibernation period may come into Hong Kong," he said.

   Tsang said the former British colony, which has seen deadly outbreaks of bird flu and severe acute respiratory syndrome, or SARS, in the past, had raised its alert level and was preparing for a possible outbreak.

   Nearly 300 people died and around 1,800 were infected when SARS spread from China to Hong Kong in 2003. Six people died and 12 others were infected in a bird-flu outbreak in 1997.