However, there is no official confirmation about Kim's visit, which, if confirmed, will be his first trip abroad since he took over power in 2011 after his father's death.
China's Ministry of Foreign Affairs said it was unaware of the issue.
Media reports about Kim's visit was in circulation following heavy police presence at the China-North Korea border and later at a Beijing hotel popular with foreign dignitaries, Hong Kong-based 'South China Morning Post' reported.
Indications suggested that a high-profile figure had made the journey into China, the Post reported today. While it is yet to be confirmed if the person is Kim himself, the security arrangements suggest it is someone of great significance, the report said.
Speculation intensified on March 27, 2018 that North Korean leader Kim Jong-Un was in Beijing for a surprise visit, after Japanese media reported the arrival of a special North Korean train met by an honour guard under tight security. / AFP PHOTO / WANG ZHAO
At the Diaoyutai State Guesthouse in Beijing, where foreign dignitaries usually stay, there has been a marked increase in police activity, with a large number of officers and about 50 vehicles seen in the area. Nearby roads have been cordoned off.
Historically, the visits of North Korean leaders to China, the country's neighbour and closest ally, were always shrouded in secrecy.
Kim's late father Kim Jong-il too used to visit China secretly.
Tensions temporarily abated in the Korean Peninsula recently over North Korea's nuclear programme after US President Donald Trump agreed for a summit meeting with Kim.
Though North Korea has remained a long-standing ally of China, relations between the two countries have been strained after Beijing beefed up UN sanctions by blocking essential supplies like oil and coal following pressure from Trump.
Observers say the severity of sanctions made Kim to tone down his rhetoric on acquiring nuclear weapons and consider the option for talks with US.