Simon Cheng did not return to work a day after visiting the neighbouring mainland city of Shenzhen.

An employee at the British consulate in Hong Kong has been detained in China for involvement in prostitution, China's state-backed Global Times newspaper said on Thursday.

China's foreign ministry confirmed on Wednesday that the employee, Simon Cheng, had been detained in the border city of Shenzhen. Britain has expressed its extreme concern about the case.

The Global Times, published by the ruling Communist Party's official People's Daily, cited in a report on its English-language website Shenzhen police as saying Cheng had been detained for 15 days for "solicitation of prostitution".

Police in Shenzhen's Luohu district said Cheng had violated article 66 of the law on administrative penalties for public security, the newspaper said.

The law stipulates that people who engage in prostitution or visit prostitutes shall be detained for no less than 10 days but no more than 15 days, and may also be fined 5,000 yuan ($705.15).

Shenzhen police declined to make any immediate comment.

Cheng did not return to work on August 9 after visiting the neighbouring mainland city of Shenzhen the previous day, Hong Kong news website HK01 reported, citing an interview with his girlfriend and family.

Cheng's family confirmed his disappearance in a Facebook post on Tuesday night, saying he travelled from Hong Kong to Shenzhen on the morning of Aug. 8 for a business trip.

Hong Kong has been gripped by anti-government protests in recent weeks, with China accusing Britain and other Western countries of meddling in its affairs.

Britain, the United States and other countries have urged China to respect the "one country, two systems" formula under which Hong Kong returned from British to Chinese rule in 1997.