BEIJING, May 31 -- Two men and three women who flew in from the United States tested positive for the A/H1N1 virus in Hong Kong on Friday, bringing the total number of infection to 20 in the city, according to Hong Kong health authorities.

    The Center for Health Protection in Hong Kong will trace patients' family members and close contacts, as well as passengers who had been on the same flights.

    As the number of imported cases increases, it won't be long before the first local case emerges in the city, said Gabriel Leung, under secretary for Food and Health.

    He said if the first local case emerges in Hong Kong, primary schools, kindergartens, nurseries and pre-schools will suspend classes for 14 days and the government will decide whether to prolong suspensions.

    All passengers arriving in Hong Kong will be required to complete a new health declaration form beginning June 1. The form requires travelers to fill in more information including their seat number on the flight, ship or vehicle, their destinations for the next seven days after arriving in Hong Kong and the transport to be used and contacts for those seven days.

    Xinhua News Agency correspondents reporting from Hong Kong.(XHTV)