Chinese regulators are investigating a Wal-Mart store in the southern city of Shenzhen for food safety violations, the official Xinhua news service reported, based on videos it said were taken by a Wal-Mart employee at one branch.
The US retail giant told Reuters that it had launched its own investigation in response to the video and found no evidence to support its claims, nor had multiple visits by authorities uncovered any wrongdoing.
"We are comfortable saying, based upon this inspection, that none of the alleged activities exists in the store today," Wal-Mart said in a statement.
The voiceover to the video – made by an anonymous person who claimed to have worked for Wal-Mart for seven years - said employees in the store's deli section, operating under the principle of "don't change for a month," would often use cooking oil so old it had turned "black as soy sauce" to cook items like fried chicken for sale to customers.
They would also fry and sell meat that had passed its sell-by date, and sell rice infested with insects, the narrator said, showing footage of black oil in a fryer, expired meat, and worms crawling on rice.
The Xinhua article said no conclusions from the investigation by the Shenzhen Municipal Market Supervisory Administration had been made. Xinhua said Shenzhen authorities were testing samples of oil and meat from the store but results were not yet available.
The statement from Wal-Mart said the company was cooperating fully with local authorities and would take "immediate actions" to deal with any issues uncovered.
The Xinhua report said that reporters had accompanied law enforcement officers to check on the operations of the Honghu branch of Wal-Mart, and found that managers had used hand-written methods to specify the shelf-lives of some ingredients.
"Handwritten expiration dates can be changed at will, leaving supermarkets plenty of room to use expired ingredients," the report said.
However, the Xinhua report also quoted a local food safety supervision official saying that at present there is no legal mandatory requirement for when frying oil must be replaced, nor is there a law against adding new oil to older oil.
The video follows a series of undercover exposes of major Western food suppliers by Chinese domestic media, many using hidden video cameras.
For example, McDonalds and Yum Brands, owner of Pizza Hut and KFC, were forced to apologise in China after being caught up in a TV expose of questionable meat-handling practices by supplier Shangha Husi Food Co Ltd.
Wal-Mart came under fire in Chinese media earlier in the year after a supplier's donkey meat product was found to contain fox meat.
In 2011 Chinese authorities accused Wal-Mart of selling expired duck meat, and it was forced to shut down stores in Chongqing after they were accused of labeling non-organic pork as organic and selling it at a higher price.