HONG KONG — The Chinese government acknowledged Wednesday that it was holding an employee of Britain’s consulate in Hong Kong who had disappeared in early August, a case that raised fears of political applications of Chinese law to combat a monthslong protest movement.
The employee, Simon Cheng, was detained while Hong Kong is in the midst of its biggest political crisis since the former British colony returned to Chinese rule more than two decades ago. His disappearance had added to fears that the police were detaining people in mainland China in an effort to intimidate supporters of the protests.
Geng Shuang, a spokesman for China’s Ministry of Foreign Affairs, said Mr. Cheng was being held under a 15-day administrative detention, without citing specifics of his alleged wrongdoing.
Mr. Cheng, 28, traveled to Shenzhen, a mainland city that borders Hong Kong, to attend a business conference on Aug. 8, but did not return as expected.
“Passing through,” he wrote to his girlfriend on WeChat, the Chinese messaging app, as he was making his way back to Hong Kong that night on a high-speed train. “Pray for me.”
Mr. Cheng was born in Hong Kong and holds a British national overseas passport, a document created for Hong Kong residents before the 1997 handover. It does not confer citizenship but does allow for consular representation outside China.
“We are extremely concerned by reports that a member of our team has been detained returning to Hong Kong from Shenzhen,” Britain’s Foreign and Commonwealth Office said in a statement on Tuesday. It added that it was providing support to Mr. Cheng’s family and trying to find out more information on his case.
Mr. Geng, the Foreign Ministry spokesman, said Mr. Cheng was Chinese, not a British citizen, suggesting that British diplomats would not be allowed to meet with him.
It was not clear whether Mr. Cheng has had any involvement in the protests. But his detention comes as China has been more vocal in blaming foreign nations, including Britain and the United States, for the monthslong protests.
The protests began over a Hong Kong government proposal that would allow extraditions to mainland China. That legislation, since suspended, raised widespread fears that Hong Kong residents could become more easily subjected to the mainland Chinese legal system, which is controlled by the Chinese Communist Party.
While the legislation specifically ruled out extradition for political crimes, many worried that mainland Chinese officials could target activists with other charges, like tax evasion or corruption.
The extradition bill continues to drive protests, but the demands have expanded to include an investigation into police use of force and an expansion of direct elections. On Sunday, organizers said 1.7 million people joined another protest march that filled streets for hours in Hong Kong.