35 restaurants across China have been found illegally using opium as seasoning in their food, state officials say.

Five restaurants are being prosecuted over the findings, whilst 30 more are under investigation, according to the China Food and Drug Administration.

The eateries include a popular chain of hot pot restaurants in Beijing.

It is unclear how the opium came to enter the food, however, previous cases in China have seen chefs try to ‘hook’ customers on their food through use of the narcotic which can cause serious addiction.

In 2014, a failed drugs test led Shaanxi provincial police to uncover a noodle seller deliberately lacing meals with opium.

In 2004, a string of 215 restaurants in the Guizhou region were closed down following similar charges.

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According to the official news agency Xinhau, poppy powder is available to buy in China at $60 or approximately £42 per kilogram.

It is commonly mixed with chilli oil and powders, which make it difficult for authorities to detect.