Beijing: The disappearance of British consulate officer Simon Cheng appears to have realised the worst fears of Hong Kong's protesters, who were first driven to the streets by the spectre of extradition to China.

Cheng, 28, has been detained by Chinese police under local law, the Foreign Ministry said on Wednesday evening. It is believed he was secreted away under the communist legal system while travelling on a new high-speed train linking Hong Kong to the nearby Chinese tech hub of Shenzhen. It controversially operates a Chinese border check within Hong Kong territory.

Cheng's family said on Tuesday evening they felt "very helpless" after it was verbally confirmed to them that Cheng had been "administratively detained" by the Shenzhen Public Security Bureau or police, but no reason was given.

Their lawyers have been unable to find Cheng, despite searching multiple detention centres in Shenzhen.