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No cases of swine flu, which first emerged in Mexico, have so far been reported in China, but the country has been the source of several previous flu outbreaks.

The Labour Day long weekend beginning on Friday is one of the biggest travel periods of the year, after the Chinese lunar new year holiday.

During the outbreak of the Sars virus in 2003, China was heavily criticised for its slow response and only belatedly introduced measures to monitor and report cases of the disease.

On Thursday government tourism officials warned the travel industry to prepare for a potential swine flu epidemic during the upcoming holiday as people who had just returned to China from affected areas could travel across the country.

"Travel agencies, hotels, scenic spots, tour buses and boats... must strengthen epidemic prevention and control measures, and make preparations to deal with a possible epidemic," the National Tourism Association said on its website.