Four Britons have been arrested in the Chinese province of Jiangsu, the British embassy in Beijing has said.
The BBC understands the arrests are part of an operation last week that saw seven foreign teachers and nine foreign students from an international education firm detained.
According to state media Xinhua, all 16 people tested positive for drug use, without specifying the drugs involved.
There are extremely severe penalties for drug offences in China.
On Tuesday, the Xuzhou Public Security Bureau, located in Jiangsu province, posted a statement on Chinese social media site Weibo saying police had successfully cracked a drug-related case.
It said it had arrested 19 people, including 16 foreigners.
It did not name the school involved, but Xinhua later confirmed that the teachers and students were from the Switzerland-based English Education (EF) First Centre.
The EF centre told Xinhua it had “zero tolerance” policy towards drugs.