China's food safety watchdog has issued further regulations to tighten supervision of baby formula, requiring producers to register and secure permits to sell their products, state news agency Xinhua reported on Friday.

The quality of milk and infant formula in China has been a sensitive topic after a series of scandals from 2008 when milk contaminated by the industrial chemical melamine killed at least six children and caused thousands to fall ill.

Consumers wary of made-in-China milk products have caused a surge in the popularity of foreign brands. In 2015, China produced 700,000 tonnes of baby formula, accounting for 65 percent of annual sales, Xinhua said.

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Under the new rules, domestic and foreign baby formula producers must register and secure permits from the China Food and Drug Administration to sell their products in China, Xinhua said. Foreign raw materials used in their products must be specified, it said.

Packaging and instructions for baby formula use will be forbidden from making health-related claims, such as "good for (the) brain", "improves immunity" or "protects intestinal tracts", it quoted the regulation as saying.

Xinhua said police arrested nine people in April implicated in the production and sale of counterfeit baby formula.