Reuters quoted on Tuesday a report by a South Korean newspaper that five North Koreans were killed and wounded two others by border guards as they defected to China.
The rare-cross border pursuit had never been done before when defectors had reached the Chinese side, according to Chosun Ilbo.
The daily added that the cross firing could have been a new instruction in dealing with defectors.
It was reported that the seven defectors had left Hyesan in Yanggang province and walked the frozen Yalu River. They crossed the Chinese border on 14 December, according to reliable sources in Changbai, Jilin province of China.
Pyongyang's guards pursued the defectors that killed five and took back to the North the two injured.
The China-Korean border is described as being calm and fairly porous. There is a constant stream of refugees and traders who come to escape scarce food in the North.
Reuters also said that the Chinese government tolerate the border traffic because of fear that Pyongyang's collapse "would turn that trickle into a flood." Beijing also anticipates Seoul and Washington troops to be stationed there.