He said he was receiving increasing numbers of accounts of fleeing North Koreans, including children, being detained in the city of Shenyang in northeastern China, and that there are signs Chinese authorities have recently strengthened their search for escapees in collaboration with the North Korean government.
He couldn't provide more specific information and said he has not discussed the matter yet with Chinese officials.
"I have been raising my concern that repatriation is contrary to the principle of non-refoulement, to which China is bound to, as repatriated North Koreans are at great risk of serious human rights violations, including torture," Quintana said at a news conference in the South Korean capital of Seoul.
Quintana also raised concerns over massive North Korean prison camps, where experts say people accused of political crimes are detained and abused without due process, and the government's suppression of media freedoms and failure to secure the people's right to food.
He spoke as North Korean leader Kim Jong Un and Chinese President Xi Jinping wrapped up a summit in Pyongyang at which they vowed stronger ties amid stalled nuclear negotiations with Washington.
Quintana said he reiterated the need to include North Korean human rights concerns in the nuclear negotiations. Following a provocative series of nuclear and missile tests, Kim began a diplomatic outreach in 2018 that led to summits with the leaders of the United States, China, South Korea and Russia. Human rights issues have been sidelined from the meetings.