Beijing (CNN) -- Chinese legislators Wednesday approved changes to the country's criminal code that will allow the police to hold certain suspects at secret locations.
The nation's state media applauded the overhaul of the criminal procedure law -- the first in more than 15 years -- as a step forward for human rights.
But critics say it leaves plenty of scope for abuses by providing more clout to China's already powerful state security apparatus.
The Chinese police have long been criticized by human rights advocates for detaining people secretly, and illegally, in so-called "black jails," often located in suburban hotels or other nondescript housing facilities.
Under the changes to the Criminal Procedure Law passed Wednesday by the National People's Congress, the police will have the authority to hold suspects for up to six months at undisclosed locations if they believe them to be involved in endangering national security, terrorism or particularly serious bribery.
"This is the formalization of detaining people wherever they please," said Nicholas Bequelin, senior researcher in Hong Kong for the nonprofit group Human Rights Watch. He noted that "endangering national security" has been interpreted in a very broad manner to include acts like criticizing the Chinese government.
An amendment to the bill last week requires the police to notify the family of a suspect being detained in this manner, but they do not have to tell the family where or for how long the suspect is being held.
The revised law, which the Chinese state news agency Xinhua said "highlighted human rights protection," provides some new rights to defendants, including access to a lawyer and the elimination of evidence gathered through torture.
"The highlight of this revision is to better embody the constitutional principle of respecting and protecting human rights," said Wang Liming, a deputy at the legislature, according to Xinhua.
But human rights advocates have expressed doubt about how thoroughly the new measures will be respected.
"The test will really be in the implementation," Bequelin said. "The police are already violating and willfully ignoring many of the defendant's rights under the law."
Chinese Internet users also raised concerns about the law on micro-blogging sites after it was passed with 2,639 NPC delegates voting in favor and only 160 voting against.
"This is such retrogression," said a microblogger using the name Luoguogg. "Can't believe I'm seeing a dark moment in history with my own eyes."
The changes to the criminal code had been years in the making, Xinhua reported, noting that opinions and suggestions had been made by different lawmakers and law enforcement departments.
The strong influence of the police, who have a dominant role in the criminal justice system in China, is holding back the prospect of meaningful reform, according to Bequelin.
"What you need to improve the justice system in China is to take power away from the police," he said.
CNN's Jethro Mullen contributed to this report.