An official at the British embassy in Hong Kong has been reportedly detained in China.
Simon Cheng did not return to work on August 9 after visited the city of Shenzhen the previous day.
News of his disappearance has been reported by Hong Kong news website HK01, which has cited an interview with his girlfriend and family.
The missing diplomat previously met with First Minister Nicola Sturgeon during a visit to China last year.
Hong Kong has been gripped by anti-government protests in recent weeks, with Beijing accusing the UK and other western nations of meddling in its affairs.
Countries such as the UK and the US have urged China to respect the “one country, two systems” formula under which Hong Kong was returned to China in 1997.
Government officials in the UK are “extremely concerned” with Mr Cheng’s disappearance.
A representative of the UK’s Foreign and Commonwealth Office said in a statement: “We are extremely concerned by reports that a member of our team has been detained returned to Hong Kong from Shenzhen.
“We are providing support to his family and seeking further information from authorities in Guangdong Province and Hong Kong.”
The Chinese Foreign Ministry declined to comment on the case, while Hong Kong police did not immediately respond to Reuters requests for comment.
Hong Kong’s Immigration Department confirmed via email it had received a “request for assistance from subject’s family member” and “had provided the family with proper advice and practical assistance."
