A Foreign Office employee detained in Shenzen has been held for violating Chinese law, according to the nation’s foreign ministry.
Spokesman Geng Shuang confirmed this in a news briefing on Wednesday morning.
Mr Cheng did not return to work in Hong Kong on August 9 after visiting the neighbouring mainland city of Shenzhen the previous day.
A Facebook post from his family, detailing his disappearance, said: “He travelled back to Hong Kong by high-speed rail on the evening of the same day, and sent messages to his girlfriend via WhatsApp and Wechat while he was about to pass customs at about 10 pm. We lost contact with him since then.”
They also spoke of being “worried sick” and feeling “helpless” over the situation.
A previous statement from the Foreign and Commonwealth Office said it was “extremely concerned” about Mr Cheng going missing.