Four Britons have been arrested in China's Jiangsu province, the British Embassy in Beijing said on Friday.
The BBC said that the arrests were part of an operation last week that saw seven foreign teachers and nine foreign students detained.
At least some of those being held are from an international language school, Education First.
Police said all 16 foreigners tested positive for drug use, but did not specify the type of drugs involved.
It is not clear what the nationalities of the other foreigners are.
"We are in contact with the Chinese authorities following the arrest of four British people in Jiangsu province, and are providing consular assistance," the Embassy added.
On Tuesday, the Xuzhou Public Security Bureau, located in Jiangsu, posted a statement on Chinese social media site Weibo saying police had successfully cracked a drug-related case, the BBC reported.
It said 19 people had been arrested, including 16 foreigners.
According to police, 18 people had been placed under administrative detention, which carries a maximum detention period of 15 days. One person was placed in criminal detention - a procedure that usually leads to a formal arrest and an indictment.
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