The United Kingdom‘s Foreign Office has said it is “extremely concerned” by reports that a staff member at the consulate in its former colony of Hong Kong has been detained in mainland China.

Simon Cheng did not return to work on August 9 after visiting the neighbouring mainland city of Shenzhen the previous day, Hong Kong news website HK01 reported on Tuesday, citing an interview with his girlfriend and family.

HK01 identified Cheng as a trade and investment officer at the Scottish Development International section of the consulate.

The report drew a swift response from the UK Foreign Office, which said in a statement released by the British embassy in Beijing that it was “seeking further information from authorities in Guangdong Province and Hong Kong” over the case.

There was no immediate comment from Chinese authorities on the statement, but Hong Kong police confirmed it had received a report on August 9 about a British Foreign Office employee who has been missing since crossing into China on a business trip.

Speaking at a news conference in Hong Kong, senior superintendent of Hong Kong police public relations branch, Kong Wing-cheung, said that an inquiry was under way.

He added that “for the sake of personal data” he could not disclose many details.

Political crisis deepens

The incident comes as Hong Kong, a major financial hub, faces its worst political crisis in decades.

The semi–autonomous Chinese territory has been rocked by a wave of protests since early June over a controversial proposed law which would allow the extradition of people to any jurisdiction in the world with which it currently has no existing formal agreement, including mainland China.

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Critics argued the bill was part of a wider move by Beijing to scale back the freedoms Hong Kong enjoys under the so-called “one country, two systems” principle put in place as it was handed back to China by Britain in 1997.

Although the Hong Kong government suspended the proposed legislation amid the mass protests against it, with Chief Executive Carrie Lam declaring it “dead”, it has refused to officially retract it.

The UK, the United States and other powers have meanwhile urged China to respect the “one country, two systems” formula, with protests over the extradition bill morphing into a broader movement calling for democratic reform and an investigation into alleged police brutality against protesters.

The calls have irked Beijing, which has accused both powers of meddling in its affairs and taken an increasingly hardline tone against the demonstrations.

Amid concerns it faces a direct challenge to its rule in the crisis-hit territory, China has massed troops within view of Hong Kong at a nearby sports complex in Shenzhen.

In an apparent bid to head off the unrest, Lam announced on Tuesday that she would initiate talks with critics of her government and pledged to conduct an investigation into alleged police violence.