The U.K.'s Foreign and Commonwealth Office said it is "extremely concerned" at reports that a staff member at the consulate in the former British colony of Hong Kong had been detained while returning to the city.
Simon Cheng, a Hong Kong resident, has been missing from work since Aug. 9 after he failed to return from a trip across the internal border to the neighboring city of Shenzhen.
Cheng, who is investment director for the Scottish International Development Agency under the aegis of the British Consulate General in Hong Kong, was last in contact with his girlfriend after boarding the high-speed train back to Hong Kong from Shenzhen on Aug. 8, the Hong Kong 01 news website reported.
"His girlfriend and family told reporters that Simon is believed detained by the mainland authorities," the report said, citing his girlfriend as saying that he is in administrative detention, a sentence that can be handed down for up to 15 days without trial, or later converted into more prolonged forms of detention if the authorities wish.
Speculation was rife on social media that Cheng may have gone missing while in the controversial dual checkpoint area of the West Kowloon high-speed rail terminus, which was designated part of the People's Republic of China in a controversial move amid fears of cross-border arrests and detentions within Hong Kong's borders.
The issue of whether or not mainland Chinese police can directly arrest and charge residents of Hong Kong also lies at the heart of the anti-extradition protests that have rocked the city since early June.
"We are extremely concerned by reports that a member of our team has been detained returning to Hong Kong from Shenzhen," a Foreign and Commonwealth Office spokesperson said in a statement.
"We are providing support to his family and seeking further information from authorities in Guangdong province and Hong Kong," it said.
The Hong Kong Immigration Department has also confirmed they have received an assistance request from Cheng’s family, and are following up on the case with the Hong Kong Economic and Trade Office in Guangdong, currently in the form of a missing persons inquiry.
Cheng's girlfriend, who gave only a surname Lee, said he had boarded the high-speed train back to Hong Kong after attending a business meeting in Shenzhen on Aug. 8.
In the last texts she received from him, Cheng wrote: "On the high speed train still," before writing "Crossing the border. Pray for me."
Police officers in the report room of Hong Kong's Wanchai police station said there was no record of Cheng's arrest across the whole of Hong Kong.
The Chinese Foreign Ministry declined to comment on the case, with spokesman Geng Shuang saying he was unaware.
The Scottish government said it was in contact with the Foreign Office about the case.
"We are aware of this incident and we are concerned for Mr. Cheng's welfare," it said.
Cheng's 'disappearance' comes amid a war of words between the ruling Chinese Communist Party and the U.K., which Beijing has accused of interfering in Hong Kong by supporting the ongoing anti-extradition protests, and of treating the city as if it were still a British colony.
Reported by RFA's Cantonese Service. Translated and edited by Luisetta Mudie.