BEIJING - China banned U.S. poultry imports today to ease growing fears about bird flu, announcing in an emergency notice that any American fowl that have already arrived at its ports would be returned or destroyed.

China's ban on U.S. poultry follows similar bans by Japan, Malaysia, Singapore and South Korea, after officials in the U.S. state of Delaware reported a mild form of avian flu in a flock there.

Prompt reaction to the Delaware outbreak likely prevented the flu from spreading, according to Corrie Brown, an infectious animal disease expert at the University of Georgia's College of Veterinary Medicine. Tests showed nearby flocks to be free of the disease, Delaware officials said. Further test results were pending.

According to China's Agriculture Ministry, in 2003 the country's total import of poultry meats and products was 709,000 tons - 96 percent of which came from the United States.

That's a small fraction of China's poultry market; the country produced more than 9.9 million tons of chicken meat alone last year - 20 percent of total worldwide production.

China itself is a large chicken-farming country, and a more dangerous form of bird flu is confirmed or suspected in 14 of the nation's 31 far-flung regions.

Today, China confirmed a previously suspected case in its remote northeastern region of Xinjiang, which is more than 1,200 miles from the site of its first confirmed case in the far south.

China has slaughtered millions of fowl to try to contain the disease's spread and inoculated millions more.

No human cases have been reported in the country, although at least 19 people have died from the disease in Thailand and Vietnam in recent weeks.

China has already banned poultry imports from those countries, as well as other flu-hit areas.

In December, China banned beef products from the United States after a case of mad cow disease was reported there. That prohibition has not been rescinded.

Henry Niman, a Harvard University Medical School instructor and a frequent critic of government SARS responses, said today he was skeptical that there were no human cases in a nation of 1.3 billion people with so many poultry infections.

"The idea that there are no human cases in China just doesn't really ring true," said Niman, who moderates a widely read e-mail list about SARS and launched its bird-flu equivalent this week.

"It seems that they've got the virus pretty widespread and it's been around for some time," he said. "That leads me to believe that there's more going on in China that the outside world knows about."

The WHO's representative in Beijing also has voiced concern that China may already have human cases of bird flu.

Emphasizing the government's effort to reassure its citizens about food safety, China's agriculture minister joined a parade of officials insisting the poultry supply is safe overall - and backing up their claims by eating chicken publicly.