Britain's foreign office said it was seeking more information about reports that a Hong Kong staff member had been detained in mainland China.
"We are concerned by reports that a member of our team has been detained while returning to Hong Kong from Shenzhen," a Foreign and Commonwealth Office spokesperson in Beijing said in an emailed statement.
"We are providing support to their family and seeking further information from authorities in Guangdong Province and Hong Kong."
Simon Cheng, an employee at the UK consulate in Hong Kong, did not return to work on August 9 after visiting Shenzhen the previous day, Hong Kong news website HK01 reported, citing an interview with his girlfriend.
The UK consulate in Hong Kong did not immediately respond to a request for comment.