No details have been provided about the circumstances of the arrests in Jiangsu province, but it comes after police in Xuzhou city said they had arrested 19 people – including 16 foreign nationals – on drug-related charges.
Police have not identified any of the suspects, but local media reported that seven of the foreigners were teachers at an education institute and nine were students.
Chinese state radio reported that some of those arrested worked at an English centre run by Education First, a Swiss firm that runs language courses around the world.
In a statement to Reuters, the company said it deeply regrets the incident and was cooperating with authorities, but has not commented on the nationalities of those involved.
The Foreign Office said that it is “in contact with Chinese authorities” over the arrests of the four Britons, and that it is “providing consular assistance”.
On its travel advice website, the UK government warns of “extremely severe penalties for drugs offences in China, including the death penalty”.
Canadian national Robert Lloyd Schellenberg was sentenced to death earlier this year after being convicted of being an accessory to drug smuggling. The case – which was a retrial – was widely considered to be in response to an executive from Chinese tech giant Huawei being arrested in Vancouver.
In 2009, China executed Briton Akmal Shaikh for smuggling heroin, despite protests that he was mentally ill.
The arrests come amid deteriorating relations between Britain and China, with the two having clashed over the recent protests in Hong Kong.
Foreign Secretary Jeremy Hunt has repeatedly called for Beijing to honour its agreements on the former British colony, where people have been demonstrating over an extradition bill.