Xinhua, the official Chinese news agency, confirmed Kim's visit after a flurry of reports from South Korean media that a train appearing to be carrying a senior North Korean official had passed through Dandong, a Chinese city on the border with North Korea.
The visit coincides with what is believed to be Kim's 36th birthday and follows a 2018 filled with unprecedented travel for the young dictator.
Instead, Kim may be seeking to gauge China's attitude toward sanctions ahead of the talks, including what North Korea would have to concede in order to win Beijing's support at the United Nations.
After years of cool relations following Mr Kim's assumption of power 2011, ties have improved remarkably over the past year as Mr Xi seeks to maintain his influence in the region.
"Xi also gains from a summit with Kim - and the timing could not be any better", said Harry Kazianis, director of defence studies at the Center for the National Interest, a USA think tank. "We are aware of the fact that Kim is visiting China, and we are closely monitoring the situation", Moon's office said.
Kim's four-day visit comes after he expressed frustration in his annual New Year's address over the lack of progress in negotiations with Washington since his unprecedented summit with Trump in Singapore seven months ago.
Kim's trip comes as the USA and North Korea look to settle the North's decades-long pursuit of a nuclear arsenal.
The Sino-North Korean rapprochement that began previous year saw both sides emphasizing the enduring historic nature of the relationship between the two countries.
Chinese foreign ministry spokesman Lu Kang gave no details about Kim's schedule or China's role as an intermediary between the US and North Korea. The train was expected to pull into Beijing on Tuesday morning, the South Korean news agency Yonhap reported, citing an anonymous source.
His visit to Beijing, which is stated to be closest ally of Pyongyang, comes at a time when China itself is locked in a trade war with the USA over Trump's demand to reduce the United States dollars 375 billion trade deficit with the US.
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Likewise, Noh Kyu-duk, the spokesman of the South Korean Foreign Ministry, said Tuesday, "Our government is continuously working to push for inter-Korean, North-China and North-U.S. exchanges and denuclearization negotiations to happen in a mutual, virtuous cycle".
It was the first time US and Chinese officials have met face-to-face since US President Donald Trump and Chinese President Xi Jinping (習近平) agreed to a tariff truce in Argentina on December 1. "Analysts believe North Korea is betting everything on a second summit with Trump, where they will try to manipulate him into making more concessions". North Korea insists that Washington first build trust by lifting the sanctions imposed on that country.
"It certainly has hurt the Chinese economy", Ross told CNBC, adding that China exports many more goods to the United States than the other way around.
US and Chinese officials are also holding trade talks in Beijing this week after agreeing on a temporary truce to their trade war last month.
"But Kim Jong Un's visit to Beijing could indirectly show President Trump that although China has maybe less economic cards, China still has some strategic and diplomatic cards", Shi said.
"China has always supported both sides to continue to hold talks and to reach a positive outcome", Lu said.
"The Chinese have been very clear to us that these are separate issues", Pompeo said.
As talks with the United States stall over ending North Korea's nuclear weapons program, a question hangs: Will he and Trump meet again? "China has actually been a good partner in our efforts to reduce the risk to the world from North Korea's nuclear capability".
But despite a cooling of relations past year with China over the imposition of sanctions, China has and remains its most important economic and diplomatic ally.