HONG KONG — The recent disappearance of five men tied to a publisher of provocative books about China’s top leaders has alarmed many people in this semiautonomous city, some who fear that the historic agreement guaranteeing the former British colony its separate government and legal system may have been dealt a severe blow.

In the worst-case scenario being speculated about, the five were all kidnapped by emissaries of Beijing and are being held in mainland China, to suffocate their voices and ferret out their Chinese sources.

On Wednesday, Lee Bo, an editor at the publishing house, Mighty Current Media, whose wife is one of its three owners, became the latest to vanish. He was last seen that day leaving a warehouse here.

On Saturday morning, he called his wife, Choi Ka Ping, from Shenzhen, across the border in the mainland, saying he was assisting in an investigation, according to Bei Ling, a writer based in the United States who has been following the case and who talked to Ms. Choi.