BEIJING — A Hong Kong-based book publisher with Swedish citizenship who was secretly spirited to China and held in custody for two years, igniting international controversy, has disappeared again in dramatic fashion — snatched from a train bound for Beijing under the eyes of two Swedish diplomats.

The bookseller, Gui Minhai, became a symbol of the Chinese government’s determination to smother criticism from abroad when he was one of five Hong Kong booksellers who disappeared in 2015, and then resurfaced in China in police custody.

Mr. Gui, who vanished from a vacation home in Thailand, was accused by Chinese state news media outlets of publishing books that slurred Communist Party leaders. Months after his disappearance, he appeared on state television confessing culpability for a drunken driving death more than a decade earlier.

Mr. Gui was formally freed from detention last October. But he has been kept in China and forced to report regularly to the police, his daughter, Angela Gui, said by telephone from Britain, where she is a graduate student.