BEIJING, Jan. 16 (Xinhua) -- China's Ministry of Health has ordered health organizations across the country to strengthen prevention and control of the norovirus infection, commonly known as "stomach flu".

    Although the rate of infection was about average this year, experts said there was a high probability of it spreading in China after recent outbreaks in Japan, Europe and the United States.

    Norovirus is one of the most common gastrointestinal viruses affecting humans and is contagious. Its symptoms include nausea, diarrhea, vomiting and abdominal cramps.

    Symptoms usually appear within 24 to 48 hours of exposure, and typically last for one to three days.

    The ministry required hospitals to quickly report abnormal increases of diarrhea cases.

    Monitoring should be strengthened in restaurants, schools, public places, construction sites and places with migrant workers, said the ministry circular.

    The ministry also asked health organizations to strengthen links with border checking departments to report epidemic situations to each other.

    Experts warned the public to be aware about food safety. They said the best way to avoid infection was to eat less raw food, especially sea food such as oysters.

    In the fall of 2006, there were massive outbreaks of the norovirus infection in Japan, Singapore and Italy, with 357,600 people contracting the virus in less than two months.