Rumors of another visit came late Monday night as a North Korean train passed into the Chinese city of Dandong under heavy security.
Kim, accompanied by his wife and top North Korean officials, was "warmly seen off by leading officials of the Party, government and armed forces organs at the railway stations", North Korea's state news agency announced. It's Kim's fourth visit to China in a year.
Kim's visit to North Korea's most important economic and diplomatic ally, which was first reported by South Korean media, follows reports of advanced negotiations for a second summit between Washington and Pyongyang aimed at resolving the standoff over North Korea's nuclear program.
Kim and Trump pledged to work towards denuclearisation at their landmark June summit in Singapore, but the agreement was short on specifics.
Kim traveled to China - his most important security and trade partner - before meetings a year ago with Trump and South Korean President Moon Jae-in.
Kim said in his New Year speech he was ready to meet Trump any time to achieve their common goal of denuclearisation of the Korean peninsula. "The US is very clear about China's position", he said, reaffirming China's commitment to reach a trade deal with US benefitting both the countries.
Kim may be trying to get a "temperature check" of China's support for sanctions against North Korea, said Harry Kazianis, director of defense studies at the Center for the National Interest, according to the South China Morning Post.
In a New Year's speech, Kim warned Washington the country might be forced to take an alternative path if the U.S. China clearly anticipates receiving a privileged stake in North Korea, Inc. when it opens for business after sanctions are eased, an outcome USA policymakers will doubtless see as preferable to all-out war on the Korean Peninsula or a nuclear holocaust.
Culminating in late 2017, Pyongyang carried out six nuclear tests and launched rockets capable of reaching the entire USA mainland, but has now carried out no such tests for more than a year.
Also, China and Russian Federation - both the permanent members of the UN Security Council - have been putting pressure on the USA to lift UN sanctions against North Korea.
More airport security screeners calling off work amid shutdown
In the midst of the stress of traveling, it can be easy to forget the reason why there may be delays in the first place. That could end up hurting air travelers if security checkpoints turn into "chokepoints".
Chinese news agency Xinhua reported that Kim will remain in the country until Thursday.
"We are negotiating a location", Trump told reporters. But the current North Korean leader shows no sign of an aversion to taking to the air.
Singapore enjoyed great publicity and financial gains as the host of the historic summit between Trump and Kim in June previous year.
Washington is pressing the North to offer up a detailed accounting of its nuclear arsenal, while Pyongyang says it has already done enough and it is time for the United States to ease harsh global sanctions that hold back the North Korean economy. However, Xi has called on the sides to "meet each other halfway", and China's foreign minister in September urged some form of sanctions relief in response to any positive outcomes from the first Kim-Trump summit.
Kim's visit comes as a USA delegation opened a second day of talks with Chinese counterparts in Beijing aimed at ending the bitter trade war between the world's two largest economies.
"Their behaviour has demonstrated that as well and we appreciate that", Pompeo said.
Kim is expected to stay at the highly secure Diaoyutai State Guest House in the capital's west, with meetings held at the Great Hall of the People, the hulking seat of the legislature that sits next to Tiananmen Square.
North Korea has held off on additional nuclear weapons and missile tests for more than a year, possibly in response to China's displeasure, while carrying out its new diplomatic offensive.
A declaration to end the Korean War, a formal peace treaty and the establishment of bilateral relations between North Korea and the United States are seen as the kind of security guarantees that can be offered by Washington to Pyongyang if it denuclearizes. "China has actually been a good partner in our efforts to reduce the risk to the world from North Korea's nuclear capability".