The reports said a train like the one often used by Kim was seen crossing through the Chinese border city of Dandong late Monday amid heavy security.
"Kim's confidence stems from the expectation of growing and reliable support by China", Rudiger Frank, a professor of East Asian economy and society at the University of Vienna, wrote on the North Korea-watching 38 North blog on January 2.
"Kim is eager to remind the Trump administration that he does have diplomatic and economic options besides what Washington and Seoul can offer", Harry J. Kazianis, Director of Defence Studies at USA -based Centre for the National Interest said in an e-mailed statement.
Mr. Kim held three summits previous year with Mr. Xi, his most important ally, before and after summits with Mr. Trump and South Korean President Moon Jae-in.
In a personal letter to Moon last month, he expressed disappointment for not making a trip to Seoul by the year's end and hoped to fulfill his promise soon.
"With the Trump administration, the [US's] relationship with China has really gone very sour, and moreover as the Trump administration ramped up its North Korean contacts they did that without an effort to bring China in - and China is a very substantial country with 1.4 billion people and they really don't want to be ignored", he told Al Jazeera.More news: Bulls trade Justin Holiday to the Memphis Grizzlies
Denuclearisation talks between the North and the U.S. have stalled, but speculation has mounted of a potential second summit between Kim - whose birthday is reportedly on Tuesday, although that has never been confirmed by Pyongyang - and Trump.
Trump said the United States had "a very good dialogue" with North Korea, adding that he had "indirectly spoken" with Kim.
A former North Korean diplomat who defected to the South urged a former colleague missing in Italy to come and settle in Seoul on Saturday, as the rare asylum bid makes global headlines.
The North Korean leader also met with Xi after the June summit with Trump.
In 2015, a counsellor in charge of science affairs at the North's embassy in Germany defected with his wife to an unidentified country, while a secretary-level trade official stationed in Bulgaria and his wife also fled, Thae told South Korean cable news Channel A in an interview this week. "The three summits with Xi Jinping in 2018 seem to have made Kim Jong Un very optimistic". North Korea is notoriously secretive about such matters.
Kim's regime, however, has been bogged down by worldwide sanctions caused by past nuclear and missile tests.
"Let's join hands in Seoul and topple the vested powers in the North and unify our nation", Thae added.