China has been pushing its reclusive and impoverished neighbor to resume talks, though Seoul, Washington and Tokyo say that Pyongyang must first show it is serious about denuclearizing.
North Korea has also flouted past agreements over its nuclear weapons ambitions and is unlikely to give up efforts to build an atomic arsenal it sees as a bargaining tool with the outside world.
Kim, who pledged earlier this week during a visit to Russia that he wanted to return to talks, said he was committed to the aim of a nuclear-free Korean peninsula, during talks in northeastern China with top Chinese diplomat Dai Bingguo.
"The DPRK adheres to the goal of denuclearization on the Korean Peninsula and is ready to fully implement the September 19 joint statement along with all sides for maintaining and promoting peace and stability on the Korean Peninsula," Xinhua paraphrased Kim as saying.
The September 19 Agreement in 2005 spelled out a process in which North Korea will scrap its nuclear programs in exchange for economic and energy aid and diplomatic relations with the United States and Japan.
North Korea is "willing to resume the six-party talks without preconditions," Kim said, referring to the talks which bring together both Koreas, China, Russia, Japan and the United States.
The Democratic People's Republic of Korea is North Korea's formal name.
While in Russia, Kim promised to consider suspending nuclear arms tests and production if international talks on Pyongyang's atomic program resume, a Kremlin spokeswoman said.
The pledge, made at talks with President Dmitry Medvedev, was intended to improve the chances of reviving the six-nation aid-for-disarmament talks that collapsed when North Korea walked out of them in 2008.
The secretive Kim journeyed to China as recently as May, but his visits are usually cloaked in official secrecy until nearly over. This time, however, Chinese state media has reported on the trip -- his fourth since May last year.
As during his previous visit this year, Kim was taken to visit places that may offer lessons for his own tattered and top-down controlled economy, in the form of booming and modern Chinese industrial sites.
He visited factories and a major dairy producer in northeastern China's Heilongjiang province, Xinhua said.
"Every time I visited China, I can feel the friendly affections from the Chinese people to the Korean people," it quoted him as saying. "I've seen new changes every time I came here."
State television showed pictures of a healthy-looking Kim laughing and smiling during talks with Dai, and being hugged by an unidentified official upon his arrival by train in China.
Kim has been looking healthier after seeming to be frail just over two years ago following a stroke, prompting speculation his rule may last longer than many had imagined.
China is isolated North Korea's main source of economic and diplomatic support, and Kim has been seeking help from regional powers for his isolated nation, which is struggling with economic hardship and food shortfalls.
"Along with our DPRK comrades, we are willing to earnestly implement important consensus reached by the top leaders of our two countries and promote the continuous growth of our ties," Dai told Kim, according to Xinhua.
Beijing has shored up its support for Pyongyang in the past two years, despite regional tension over North Korea's actions, including nuclear weapon tests in 2006 and 2009 that drew U.N. sanctions backed by China.
When Kim visited China in May, the two sides vowed that their alliance, "sealed in blood," would pass on to their successors.