At least 13 refugees from North Korea have been arrested in the southwestern Chinese city of Kunming while they were trying to reach South Korea, media reports said Monday.

Chinese police on Friday arrested the 13 who were trying to board a bus bound for an unidentified Southeast Asian nation, Yonhap news agency said.

It cited South Korean activists promoting human rights for North Korean refugees.

Dong-A Ilbo newspaper also reported the arrests but put the number 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.

"It appears that they were trying to save money for hiring brokers who could help them cross the border."

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 or repression at home to settle in the capitalist South over the past six decades.

Almost all cross the North's border into China. Many of them then secretly travel through China to a third nation -- often in Southeast Asia -- where they arrange to fly on to South Korea for resettlement.

China -- the North's sole major ally -- considers the fugitives to be illegal economic migrants instead of refugees and repatriates those whom it catches.

Rights groups strongly criticise Beijing's policy. The fugitives can face severe punishment including a term in a prison camp once they are sent back to the North.

Asked about the South Korean reports at a regular briefing, China's foreign ministry spokesman Qin Gang said: "These people that you have mentioned are not defectors from the DPRK (North Korea), they are illegal border crossers. In dealing with relevant issues we have always abided by domestic law, international law and humanitarian spirit."

Asked if he was confirming the detainees were North Koreans, he said: "I'm not aware of the specific issue as well as the specific persons involved in the issue."

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 percent 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.