Last week, Trump received another letter from Kim. South Korean news channel YTN reported early Tuesday morning that Kim Jong-un was on board the train, but no official confirmation yet from China or North Korea's state media outlets.
"We are negotiating a location", he told reporters before boarding a helicopter for the presidential retreat at Camp David, Maryland, where he said he would be discussing a trade deal with China.
Kim, whose family has ruled North Korea with an iron fist for 70 years, wants immediate economic benefits and a formal end to the 1950-53 Korean War.
On previous occasions when Kim Jong Un has traveled to China to hold meetings with President Xi, the North Korean leader made the journey in a distinctive armored green train such as the one observed on Monday.
Kim started off his flurry of summits past year with a meeting with Xi.
Rumors about Kim's visit to China began late Monday local time when a North Korean train painted green carrying a "senior North Korean official" was described crossing over the North Korea-China border, South Korea's Yonhap News Agency reported.
US President Donald Trump on Sunday said he has been in indirect contact with Kim Jong-un and his talks with the North Korean leader have averted a major war in Asia.
Kim previously met with Xi in 2018 on three different occasions, which took place before and after the historic meetings with US President Donald Trump and South Korean President Moon Jae In. Korean language watermark on image as provided by source reads: "KCNA" which is the abbreviation for Korean Central News Agency. The two leaders are expected to meet soon.
Negotiations were underway on the location of their next meeting, Trump said Sunday, while remaining evasive on its timing.
"If he's going to denuclearize, we have to be sure the I's are dotted and the T's are crossed because there are ways to hide like we all know", said Senator Dianne Feinstein. "They do want to meet and we want to meet and we'll see what happens".
Culminating in late 2017, the North has carried out six atomic blasts and launched rockets capable of reaching the entire United States mainland, but has now carried out no such tests for more than a year.