The cable from US ambassador to Seoul Kathleen Stephens describes a widening gap between the governments of China and North Korea.
It signals China could not stop the collapse of the ailing dictatorship after the death of its leader Kim Jong-Il.
Ms Stephen's cable is dated February 22, 2010 and given the second highest security classification Secret.
It quotes South Korean Vice-Foreign Minister Chun Yung-woo saying China expects a political meltdown in North Korea within three years of Jong-Il's death.
There is "no will" to increase Chinese economic investment and influence in the country to force a change in its policies, he is quoted saying.
"China had far less influence on North Korea "than most people believe."
Beijing had "no will" to use its economic leverage to force a change in Pyongyang's policies and the... leadership "knows it," the cable says.
Mr Yung-woo also cites two "sophisticated" unnamed Chinese officials who are "ready to face the new reality" that North Korea had little value to China.
New trade and labor-export opportunities for Chinese companies would help salve concerns about a reunified Korea, he said.
"Describing a generational difference in Chinese attitudes toward North Korea, Chun claimed (unnamed official) believed Korea should be unified under ROK control," the cable says.
More than 251,000 diplomatic cables are being released by whistleblower Wikileaks.
Wikileaks: China Moving Away From North Korea
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