China has been scrambling to right its gargantuan processed-food ship ever since six infants died and thousands more were hospitalized with kidney damage in 2008 from milk adulterated with an industrial chemical.

But as the latest scandal involving spoiled meat in fast-food shows, the attempted transformation over the last six years has run up against the country’s centuries-old and sprawling food supply chain.

From factory inspections to product recalls, laboratory testing to prosecutions, China’s emergent food-quality apparatus has turned into reform on the fly, with ever-changing threats and setbacks. Now, the growing presence of big American brands means that the country’s oversight efforts — and its most glaring lapses — are playing out on a global stage.

Earlier this year, fox meat was found in packages sold by Walmart as “Five Spice” donkey meat, prompting a recall and the company’s pledge to triple its spending on food safety in China. Excessive amounts of antibiotics and hormones discovered in some chicken products sold by KFC in late 2012 led to calls for a consumer boycott; the company’s troubles deepened last year when nine deaths from avian flu raised public concern about chicken generally and depressed its sales.

“The way I keep explaining China to people is that it’s kind of like the U.S. in the time of Upton Sinclair and ‘The Jungle,’ ” said Don Schaffner, a professor of food microbiology at Rutgers University and president of the International Association for Food Protection, referring to the 1906 novel that described unsanitary conditions in the meatpacking industry and inspired reform. “There is tremendous desire by the Chinese to get it right, but they have a long way to go.”

The meat episode that started garnering widespread attention on Sunday ensnared a roster of American fast-food giants. It stemmed from a hidden-camera broadcast by Shanghai-based Dragon TV showing processing plant workers using out-of-date chicken and beef to make burger patties and chicken products. Meat that had dropped onto the floor was scooped up and tossed back into the processing machine, the news report showed.

Government investigators have since found that workers at the plant, Shanghai Husi Food, used expired or rotten meat to make Chicken McNuggets, beef patties and other food products totaling more than 5,000 boxes, the official news agency Xinhua reported. One hundred tons of meat products were seized, and on Wednesday police detained five people as part of their inquiry. The factory supplied McDonald’s, KFC and other fast-food restaurants in China, and is a subsidiary of the OSI Group, based in Aurora, Ill.

Along with McDonald’s and KFC, the restaurants that have stopped obtaining supplies from Shanghai Husi include Burger King, Starbucks and the Papa John’s pizza chain. The factory had customers in Japan as well, including McDonald’s Holdings Japan, which said it had sourced about a fifth of its Chicken McNuggets from Shanghai Husi and stopped selling the product on Monday.

As of Wednesday, regulators in Shanghai said they had conducted 875 inspection visits to 581 companies using products from Shanghai Husi.

“Company management was appalled by the report and is dealing with the issue directly and quickly” through internal inquiry and cooperation with government investigators, OSI said in a statement. A company spokeswoman declined to answer questions.

China is not alone in facing food-safety dangers. In the past week alone, a nationwide recall was issued for fruit from a California packing plant over concerns of possible contamination by the pathogen listeria, though with no illnesses as yet reported; the food company Sysco agreed to a $19.4 million settlement in California in connection with the storage of perishable food in unrefrigerated sheds; and Minnesota health officials investigated 13 cases of illness from the food-borne bacteria E coli.

Globally, millions of people fall ill every year from eating unsafe food, and the World Health Organization estimates that food- and waterborne diseases lead to about 2.2 million deaths annually.

But the oversight efforts are mixed in China. The country has banned or limited sales of imported American foods including pork, citing concerns about feed additives, even as it grapples with recent safety concerns over contaminants in an array of its domestically produced rice, bottled water and soy sauce.

It is difficult to gauge just how much progress China is making given its still-nascent efforts to create a system of public health epidemiology that can trace food-borne illnesses back to their source, food safety experts said. By contrast, the Centers for Disease Control and Prevention in the United States is viewed as having perhaps the world’s most vigorous food-borne illness detection system, which may account for much of the continuing product recalls and alerts involving American products.

The varied and often-stomach-turning episodes in China, along with the growing number of American food companies operating there, have made it a focus of world attention and expert support in the efforts to build its food-quality protections. Events like the government-sponsored China International Food Safety and Quality Conference, which began eight years ago, have been drawing top American experts, from regulators to litigators, who say the challenge China faces is staggering.

“Although China is by outward appearance an incredibly modern and vibrant society, it just doesn’t have a long history of regulatory control, of checks and balances, where somebody is making the decision, ‘If the meat falls on the floor, should I put it back in?’ ” said Bill Marler, a Seattle-based consumer lawyer who has attended the food safety conferences.

Mr. Marler, a leading filer of food-borne illness lawsuits in the United States, cites the lack of a vigorous civil torts system in China as a major hindrance to its food-safety overhaul, arguing that big-dollar cases cause companies to change their ways. But the failings in China’s system range widely, observers said, and persist despite the 2009 update of its Food Hygiene Act with the far-more vigorous Food Safety Law.

There may prove to be a benefit as more American food companies enter the Chinese market. While they are raising public alarm about episodes like this week’s meat scandal, they may also come bearing the expertise to help set things right, Professor Schaffner said.

“They’re not perfect,” he said. “But when companies like McDonald’s and Yum Brands come in, they are bringing high food-safety standards to China, which is good for Chinese suppliers.”