The Lunar New Year travel period in China has officials bracing for a possible new wave of swine flu infections as crowded conditions create the ideal mechanism for the virus to spread.
Tens of millions of Chinese take to the rails, roads and air during the most important holiday of the traditional calendar. The holiday period this year runs from late January into February.
A Health Ministry bulletin on its Web site says "Disease prevention measures must remain rigorous."
China has already taken severe measures to control the spread of the virus, including quarantining large numbers of travelers.
The ministry says China, with 1.3 billion people, had more than 120,000 cases of infection by the end of December, including 648 deaths.
The ministry says it has not discovered mutations in the virus or the emergence of drug-resistant strains.