Health experts have assured consumers that Chinese pork is still safe despite reports of pigs being infected with the deadly A/H1N1 flu.

Swine at a slaughterhouse in Heilongjiang province tested positive for the virus last Thursday, the Ministry of Agriculture revealed over the weekend.

Four positive samples were discovered at the abattoir in Shuangcheng by a local flu laboratory, China News Service quoted a ministry statement as saying.

Officials suggested the cause of infection could have been the animals' close contact with humans during transportation.

Gene sequence analysis showed the virus suffered by the pigs is a 99-percent match with the human H1N1 strain. No mutation was found, the government statement said.

It is the first such infection in China, although there have already been reports in 13 other countries and regions, Beijing Times reported yesterday.

However, experts with the World Health Organization (WHO) insisted well-prepared pork is still safe to eat because the virus cannot survive temperatures of 70 C and above.

China consumed more than 46 million tons of pork last year, around half of the world's total.

Since the outbreak of H1N1 in April, prevention and monitoring of swine has been a priority for the government. The virus was originally known as "swine flu" before it was renamed to dispel any links with pigs.

The information office of the Ministry of Agriculture was unable to comment yesterday, but in a statement last week officials said authorities across China had checked about 87 million pigs, but no influenza virus had been detected.

Meanwhile, four patients in North Carolina in the United States tested positive over the weekend for a new H1N1 strain that is resistant to oseltamivir, or Tamiflu, AP reported.

Tamiflu is one of two flu medicines being used in the fight against H1N1 and health officials have been watching for signs of the virus mutating, making the drugs ineffective.

More than 50 resistant cases have been reported since April, including 21 in the U.S.. Almost all in the U.S. were isolated, officials with the U.S. Centers for Disease Control and Prevention said.

London-based BBC reported five Tamiflu-resistant cases in Wales last week.

The Norwegian Institute of Public Health also said it had detected mutations in three positive samples. The viruses were isolated from the country's first two fatal cases and one other patient.

Norwegian scientists have analyzed samples from more than 70 patients, but only in three have mutations been detected. This suggests the mutation is not widespread, say scientists.

Laboratories in Brazil, Japan, Mexico, Ukraine and the U.S. have all detected similar mutations, with the earliest being in April.

Although information is incomplete, the mutations were detected in fatal, as well as mild cases. Experts said the significance of the finding is unclear.

As of Friday, the virus had killed 6,770 people worldwide since April, with 520 deaths in the past week, according to figures released by the WHO yesterday.