BEIJING - China has detected eight cases of swine flu mutation, a health official said Wednesday, amid longstanding concerns among scientists that the virus could change into a more dangerous form.

Last week, the World Health Organization said it was investigating samples of variant swine flu linked to two deaths in Norway.

But Shu Yuelong, director of the Chinese National Influenza Center, told the official Xinhua News Agency that the mutated swine flu virus found China has shown an "isolated" spread in the mainland, is not resistant to drugs and can be prevented by vaccines.

The report did not provide any more details, such as when the cases were detected and if they were linked to any deaths. Calls to the National Influenza Center rang unanswered while the Health Ministry did not immediately respond to a faxed list of questions.

Swine flu has triggered a global pandemic, and scientists are worried that swine flu could mutate into a more dangerous or more infectious form or swap genes with seasonal or other types of flu.

On Friday, the WHO said it was looking into two deaths and one severe case linked to variant swine flu in Norway, after that country's Institute of Public Health announced that the mutation could possibly cause more severe disease because it infects tissue deeper in the airway than usual.

The same mutation has been found in both fatal and mild cases elsewhere, including in Brazil, Japan, Mexico, Ukraine, and the United States, said the WHO.

WHO's spokeswoman in Beijing, Vivian Tan, said the agency is aware of three such cases in China that occurred in June and July that were similar to the cases being investigated in Norway. Tan said WHO had no information on the cases mentioned in the Xinhua report Wednesday.

There is no evidence the mutated swine flu virus is circulating widely in the world, Tan said, but since it has been linked to deaths in Norway and elsewhere, investigators are focusing on whether this mutation could be a marker for more severe disease.

"We are concerned, but realize that influenza viruses, including A/H1N1, are relatively unstable and change easily, especially as they infect more people," Tan told The Associated Press. "Some mutations can have minimal effects on how a virus functions, while other mutations can create important changes with significant public health impact."

China's Health Ministry said Wednesday that 51 swine flu deaths were reported last week, bringing the total number of fatalities in the country to 104.