The group made the claim in a report, "We Are Afraid to Even Look for Them: Enforced Disappearances in the Wake of Xinjiang's Protests."
"The cases we documented are likely just the tip of the iceberg," said Brad Adams, Asia director at Human Rights Watch. "The Chinese government says it respects the rule of law, but nothing could undermine this claim more than taking people from their homes or off the street and 'disappearing' them -- leaving their families unsure whether they are dead or alive."
Hundreds of people were arrested during massive protests in July in Urumqi and other cities in the Uighur Autonomous Area. The Uighurs are mostly Muslim and ethnically distinct from Han Chinese, and there is an active independence movement.
Chinese officials charge some of those arrested are guilty of murder and arson. Nine men have already received death sentences since trials began last week, two were sentenced to death with two-year reprieves and one to life in prison.
2014: The Year in Music [PHOTOS]