Chinese police have detained a US automotive engineer since November last year on accusations he misused trade secrets — the latest case of vague secrecy laws being used against an American in China.

Hu Zhicheng (胡志成), a prize-winning designer of industrial catalysts to control auto emissions, has had letters from his family censored and has been denied reading materials during his detention in Tianjin, the US embassy in Beijing said. Last week police rejected an Old Testament he asked US consular officers to bring him.