BEIJING — Last Jan. 27, an Inner Mongolian rights activist, Govruud Huuchinhuu, suddenly vanished after leaving a hospital where she had undergone treatment for cancer. On Feb. 16, the Beijing human-rights lawyer Tang Jitian vanished after being forcibly taken away by police officers. On May 30, an ethnic Uighur, Ershidin Israel, vanished after being deported to China from Kazakhstan as a terrorism suspect. In the next two weeks, three other Uighurs vanished as well.

The Beijing artist and dissident Ai Weiwei, who vanished into police custody on April 3 and did not emerge until June 22, is but the most famous Chinese activist to suffer an “enforced disappearance,” as human rights officials call such episodes. Experts say 2011 has seen a sharp and worrisome increase inside China of a security tactic that a United Nations international convention has sought to outlaw.

Now China is answering complaints by rights activists that the disappearances of those and other Chinese are unlawful and potentially inhumane: It is rewriting the national criminal procedure code to make them legal.

The new proposal, drafted by a committee of the National People’s Congress, the nation’s quasi-legislature, is undergoing public review. It would amend the current code, which allows government authorities to place criminal suspects under house arrest for up to six months. The proposed revision would allow them to imprison in a secret location anyone who, under home surveillance, is found to hinder an investigation. Suspects’ families would have to be told of their disappearance within 24 hours — unless doing so would hinder the investigation of crimes involving national security or terrorism.