Seoul: A spate of murders by North Koreans inside China's border is prompting some residents to abandon their homes, testing China's ability to manage both the 1400-kilometre shared frontier and its relationship with the reclusive nation.

The violence reflects a growing desperation among soldiers, including border guards, since Kim Jong-un took over as supreme leader in Pyongyang three years ago. As well as seeking food, they are entering China to steal money.

A North Korean soldier patrols along the bank of Yalu River, near the North Korean town of Sinuiju, opposite the Chinese border city of Dandong. Credit:Reuters

"Bribes were one of the key sources of income for these guards to survive, but after Kim Jong-un came to power and tightened controls, it became difficult for them to take bribes, thus the criminal deviations," said Kang Dong Wan, a professor of international relations at Busan's Dong-a University in South Korea.

The murder of four residents of a border village last month prompted China to file a complaint with North Korea, risking tensions between the two allies in contrast to Mr Kim's recent overtures toward South Korea. Mr Kim defied China in 2013 to conduct North Korea's third nuclear test, and in the same year executed his uncle, Jang Song-Thaek, who had promoted commercial ties with China.