Chinese police on Friday arrested 13 North Korean refugees who were trying to board a bus bound to an unidentified Southeast Asian nation, Yonhap news agency said.
It cited South Korean activists promoting human rights for North Korean refugees.
Dong-A Ilbo, a major newspaper in Seoul, also reported the arrests but put the number of arrested at 15.
"Most North Korean defectors travel in a group of five at most when crossing the Chinese border to a Southeast Asian nation," said one activist quoted by Yonhap.
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A spokesman for the South's unification ministry, which handles cross-border affairs, said Seoul was trying to verify the report.
Some 25,000 North Koreans have fled famine and repression at home to settle in the capitalist South over the past six decades -- mostly after the devastating famine in the late 1990s.
Most cross the increasingly porous border with China before secretly travelling to a third nation -- often in Southeast Asia -- where they seek permission to resettle in the South.
The refugees can face severe punishment including a term in a prison camp once they return home.
The North's young leader Kim Jong-Un is believed to have tightened border controls since he took power in late 2011.
The number of refugees arriving in South Korea plunged more than 40 per cent to 1,508 last year.
A rare repatriation in May of nine mostly teenage North Koreans arrested in Laos -- previously considered a relatively safe transit point -- sparked UN criticism and concerns that Pyongyang might be stepping up diplomatic campaigns to bring back refugees from abroad.