The 55-km long bridge connecting Hong Kong, Macau and mainland China. (Image for representational purpose only)

An employee at the UKโ€™s consulate in Hong Kong has been detained by Chinese authorities on his way back to the city.

Simon Cheng, 28, was returning from a trip in Shenzhen to his native Hong Kong on August 8 when his girlfriend, Li, stopped receiving communications from him, The Guardian reported

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โ€œWe are extremely concerned by reports that a member of our team has been detained returning to Hong Kong from Shenzhen โ€ฆ We are providing support to his family and seeking further information from authorities in Guangdong province and Hong Kong,โ€ the newspaper quoted a spokesman for the UKโ€™s Foreign and Commonwealth Office as saying.

Li said Cheng had messaged her just before he went silent. โ€œReady to pass through the border โ€ฆ pray for me,โ€ he had written.

More than 10 days later, Li and Chengโ€™s family have not been able to get in touch with him. Li said Hong Kong immigration authorities told her Cheng had been placed under โ€œadministrative detentionโ€ in mainland China in an unknown location and for unknown reasons.

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The detention of Cheng, who works in the British consulate as a trade and investment officer for Scottish Development International, comes amid more than two months of pro-democracy protests in Hong Kong that have threatened Beijingโ€™s authority over the city.