The publisher of a leading magazine on Chinese and regional defense issues says he's leaving Hong Kong out of concern he could be targeted by China's state security bodies, a further sign of how Beijing's growing presence is chilling the political atmosphere in the territory.

Kanwa Asian Defense publisher Andrei Chang said Thursday that the suspected abductions to China of booksellers tied to a Hong Kong publisher of tomes about sensitive Chinese political topics had left him shocked and concerned, prompting him to decide to move to Tokyo next month while continuing to publish his magazine in Hong Kong.

"Once you know someone who'd been kidnapped, you start to wonder if you'll be next, said Chang, a Canadian citizen who was born in China and who knows the men in the case. "We have to think tactically," he said.

Chang is a top authority on the People's Liberation Army, the world's largest standing military which is fast adding cutting-edge technologies to its arsenal. He also writes about Chinese leadership issues, particularly President Xi Jinping's moves to strengthen his control over the PLA.

Hong Kongers such as Chang were stunned by the recent temporary disappearances of Swedish-Chinese author Gui Minhai and four colleagues associated with the Causeway Bay Bookstore, including his British chief editor Lee Bo. That was due in part to suspicions that mainland Chinese security agents snatched Lee and spirited him across the border, violating Beijing's promise to stay out of most local affairs including law enforcement.

Gui apparently was apprehended in Thailand and taken to mainland China.

Although many ethnic Chinese in Hong Kong, including Chang, hold foreign passports as a sort of insurance policy in case of a crisis, the difficulties Britain and Sweden faced in getting consular access to Lee and Gui raised doubts about that strategy.

Three of Gui and Lee's colleagues are now free on bail in the mainland, but the pair appear to be still detained without charge.

The case added to perceptions that China is backing away from its promise to leave the city's freedoms intact for a half-century after taking control of Hong Kong from Britain in 1997.