China should immediately reveal the whereabouts of eight North Koreans it detained last month, Human Rights Watch said Monday, adding they risk severe torture if they were returned to the North.
Most North Korean refugees begin their escape by crossing into China and then try to make it to third countries -- often in Southeast Asia -- where they seek asylum in the South.
If caught and returned to the North they can face severe punishment.
China regularly labels North Koreans as illegal "economic migrants" and repatriates them based on a border protocol adopted in 1986.
"By now, there are plenty of survivor accounts that reveal Kim Jong-Un's administration is routinely persecuting those who are forced back to North Korea," said Phil Robertson, deputy Asia director for Human Rights Watch.
The group it highlighted -- which includes at least four women -- was detained by Chinese officials in mid-March after they were stopped for a random check in Shenyang, in northeastern China.
Human Rights Watch said that on the basis of information from sources it considers usually reliable, the group was still believed to be jailed in China. But it feared they may soon be returned to the North since "most repatriations happen two months after detention".
"There is no way to sugar coat this: if this group is forced back to North Korea, their lives and safety will be at risk," Robertson said.
Seoul's foreign ministry did not confirm the HRW account, saying its protocol was not to publicly comment on individual refugee cases for their own safety and to protect diplomatic relations.
"But we closely coordinate with a nation involved when a problem involving North Korean refugees arises," it said in a statement, and was in general "doing our best to ensure the safety and safe transfer of those who wish to come to the South".
More than 40 North Koreans, including children and pregnant women, have been held by China over the past nine months, Human Rights Watch said, and at least nine forcibly returned to the North.
Since the end of the Korean War in 1953, more than 30,000 North Koreans have escaped -- most after a deadly famine in the mid-90s -- and settled in the South.
North Korean leader Kim Jong-Un is believed to have tightened border controls since he came to power after the death of his father Kim Jong-Il in December 2011.
The number of refugees arriving in South Korea plunged nearly 50 percent to 1,417 last year.