A massive adulterated food scandal has been uncovered in China that involved making fake-branded sauces and flavourings using recycled spices and industrial- grade salt harmful to human health.

The fake seasonings, sauces, stocks and powdered spices had been sold across the country under well-known domestic and international brand names including Knorr, Nestle, Lee Kum Kee and Wang Shouyi for more than a decade, The Beijing News reported.

The workshops, numbering almost 50 involved in producing them are so well-organised that they were equipped with surveillance cameras installed outside their building and residents alerting them about any strangers visiting the areas.

Local police admitted it was hard to crack down on the illegal business, the report said.

About 100 million yuan worth of the fake products are produced each year in the little town of Duliu in the Jinghai area of Tianjin, Hong Kong-based South China Morning Post quoted the report as saying.

Some producers earn so much money making the fake goods that they drive around in Porsches, it said.

Ingredients for the fake food seasonings include tap water and industrial-grade salt, which is banned from human consumption because it can contain cancer-causing agents and heavy metals that damage the liver and kidneys.

The producers make the fake-branded food seasonings by buying used spices and herbs such as star anise, pepper and fennel from melon-seed processing factories in nearby Wangkou town, drying the ingredients and grinding them into powder in dilapidated low-rise buildings, the article said.

The report said used spices were kept in disused yards at the melon seed factories with rubbish piled nearby.

A whistle-blower told the newspaper that workshops producing fake branded chicken stock used a kind of colouring banned in the food industry.

The bogus products have the same packaging as their branded counterparts. The counterfeiters copied QR barcodes on genuine products and used them on their own packaging to pass the food off as real.

The workshops hire dozens of workers and have formed a complete industrial chain ranging from procurement, processing and delivery, the whistle-blower was quoted as saying.

Some businesses had operated for about a decade. Many workshops have installed surveillance cameras on their walls to warn if their operations were under scrutiny, the report said.