HONG KONG, May 25 (Xinhua) -- A four-year-old boy and his younger sister tested positive for the A/H1N1 virus in Hong Kong on Monday, bringing the total number of confirmed cases in the city to nine, health authorities told a press briefing Monday evening.

    The two children, who returned to Hong Kong with their parents from the U.S. city of New York on Sunday aboard Cathy Pacific flight CX 841, were taken to a private clinic Monday morning after developing flu-like symptoms, said Thomas Tsang, controller of the Center for Health Protection (CHP).

    They were later sent to Queen Mary Hospital, Tsang said, adding that their conditions are now stable.

    The two children have been in close contact only with their parents and a domestic helper, all of whom showed no symptoms yet and will be soon sent to Princess Margaret Hospital for medical observation, Tsang said.

    The CHP has been working with the immigration department to trace two flight attendants and some 50 passengers sitting near the two confirmed patients, who were sitting in Row 41, Tsang said.

    The one-and-half-year-old girl had an onset of runny nose on May 23 and the boy showed similar symptoms after arriving in Hong Kong. They were not wearing facial masks on the plane and passed thermal scanning at the airport, the official said.

    The family got on a train of the Airport Express to the International Financial Center in the Central. They stayed briefly there and took a taxi to their home in Cavendish Heights, Tsang said.

    Tsang urged the taxi drivers who took the family from Central to Cavendish Heights yesterday evening and from Cavendish Heights to the clinic in Repulse Bay this morning to contact the hotline.

    He called on the public to advise their children, relatives or friends coming to Hong Kong from abroad to defer their trips if they developed symptoms such as fever, cough or sore throat.

    "To protect their own health and that of other travelers, they should seek medical attention where they are...If they feel unwell on the plane, they should wear a face mask and inform cabin crew immediately," he said.