A top Chinese envoy acknowledged Friday South Korea's "dissatisfaction" with China's policy towards North Korea, but asked for Seoul's understanding over Beijing's reluctance to punish Pyongyang.

Chinese Vice Foreign Minister Zhang Zhijun also suggested that China and South Korea should stand side by side in pushing Japan to face up to its aggressive militaristic past.

Zhang was wrapping up a three-day visit to Seoul as the envoy of China's next leader Xi Jinping that included talks with South Korean president-elect Park Geun-Hye.

During their meeting on Thursday, Park had stressed the need for South Korea and China to send a "clear and consistent" message to North Korea to abide by its international responsibilities.

Seoul is known to be frustrated with China's reluctance to approve expanded UN sanctions against Pyongyang for its long-range rocket launch last month, which most of the world saw as a disguised ballistic missile test.

"I understand some South Korean friends are dissatisfied with China's policy toward the North, but I ask them to understand China's difficulties as well," Zhang said Friday.

China is North Korea's sole major ally and has repeatedly argued that pushing Pyongyang into a corner could provoke a reaction that would seriously destabilise the Korean peninsula and the wider region.

"The greatest tragedy of the North and the South was the fratricidal conflict," Zhang said, referring to the 1950-53 Korean War.

"All the measures China has been taking so far have been aimed at preventing such a tragedy happening again," he told a breakfast meeting of businessmen and journalists.

"The chronic disease with regard to issues of the Korean Peninsula is a lack of trust," he added.

Separately, Zhang urged Japan to avoid any rightward, nationalist shift under the new premiership of the hawkish new Prime Minister Shinzo Abe.

"If Japan walks a dangerous path, it will significantly hurt cooperation among China, Korea and Japan," Zhang said.

Beijing and Seoul are involved in separate territorial disputes with Tokyo and both have long criticised Japan for failing to show enough contrition for the abuses of its military expansionist past.

"If Japan continues denying history and turning a blind eye to history, it will not be able to act with moral authority in the international community," Zhang said.

"Korea and China should stand up on this issue of history and express their positions," he added.

There is still widespread public resentment in South Korea over Japan's 1910-45 colonial rule and the plight of Korean women who were forced to serve as sex slaves for Japanese soldiers.