It is believed that all five are being held by mainland Chinese authorities over the border from Hong Kong. The Hong Kong government has reiterated its dedication to upholding legal guarantees for Hong Kong's press freedoms and the rule of law in the semi-autonomous city, which enjoys a high degree of press freedom that often irks mainland authorities.
Beijing may be testing to see how far it can encroach on Hong Kong without provoking an unacceptable backlash.
Hong Kong officials investigating the disappearances will likely be treated with indifference by mainland officials.
The incident plays into the hands of Taiwan's pro-independence opposition party in the final days before the presidential election.
Mainland tourists to Taiwan and Japan may offer alternative markets to publishers of material on China's leaders.
