A staffer at the British Consulate General in Hong Kong has been detained in the Chinese border city of Shenzhen for violating a law on public order, Beijing acknowledged Wednesday.

Simon Cheng was slapped with 15 days of administrative detention for violating regulations on “Punishments in Public Order and Security Administration,” Foreign Ministry spokesman Geng Shuang said.

He said the case was “not a diplomatic issue,” but gave no further details.

“He is not a British citizen. He is a Chinese person, so this is entirely a matter of China’s internal affairs,” Geng said.

“As for Britain’s comments, we’ve made stern representations to Britain for the series of comments and actions they’ve made on Hong Kong,” he added.

Britain has said it is “extremely concerned” about Cheng, a trade and investment officer at the Scottish Development International section of the consulate in the former British colony.

Cheng attended a business event in Shenzhen on Aug. 8 but never returned to Hong Kong despite plans to do so the same day, his girlfriend and family told local news outlet HK01.

The incident comes as relations between Britain and China have become strained over what Beijing calls London’s “interference” in pro-democracy demonstrations that have gripped Hong Kong during the past three months.

Geng called on Britain to stop meddling in China’s internal affairs.

“Britain has made a series of wrong statements on Hong Kong. We again urge them to stop gesticulating and to stop fanning the flames,” Geng said, according to Reuters.

Shenzhen police declined immediate comment to the news agency.

Max Chung, a friend of Cheng, organized a small protest against his detention outside the consulate in Hong Kong, saying Cheng had not been involved in any of the anti-government protests.

“Simon’s case has shown very serious consequences to everybody in Hong Kong,” he told reporters, urging Britain to “save Simon now.”

With Post wires