North Korean leader Kim Jong-un wrapped up his four-day visit to China on Wednesday after holding talks with Chinese President Xi Jinping and touring an economic zone, while the U.S. maintains its silence over the two leaders' meeting.
The long train was seen Wednesday travelling on an elevated track over a busy street heading toward eastern China.
Kim reportedly met Chinese President Xi Jinping during his trip, which may have been a precursor to a second summit between Kim and U.S. President Donald Trump.
Analysts say China could use the North Korean issue as a bargaining chip in the negotiations, but Beijing's foreign ministry rejected any link between Kim's trip and the talks.
The unannounced trip was largely shrouded in secrecy.
In a report also on Thursday, North Korea's state media KCNA said that Kim and Xi had in-depth discussions on how to "jointly study and steer" the situation on the Korean Peninsula and denuclearisation talks.
Kim held three summits previous year with Xi, his most important ally, before and after summits with Trump and South Korean President Moon Jae-in.
Progress between Washington and Pyongyang has always been hobbled by wide differences on how denuclearisation should unfold, and under what conditions.
China's official Xinhua news agency confirmed that Kim was visiting from Monday to Thursday at Xi's invitation.
Xi has yet to visit North Korea since taking office in 2012.
Mr Moon, who has over the past year played mediator between North Korea and the U.S., said at a news conference on Thursday that Seoul would cooperate with the United States in resolving the issue of sanctions on North Korea.
He also credited President Xi Jinping with helping reduce regional tensions, saying "the Korean Peninsula situation has been easing since past year, and China's important role in this process is obvious to all".
Xi and first lady Peng Liyuan later hosted a dinner for Kim and his wife Ri Sol-ju at Beijing's Great Hall of the People, which lasted four hours.
"We always believe that, as key parties to the Korean Peninsula issue, it's important for the two sides to maintain contact and we always support their dialogue to achieve positive outcomes, " Lu told reporters.
Mr. Kim's visit also came after he expressed frustration in his annual New Year's address over the lack of progress in negotiations with Washington since the Singapore summit with Mr. Trump in June, saying that if things don't improve meaning that if sanctions relief and security guarantees aren't in the offing Pyongyang might have to find "a new way" forward.
But Hua said Kim's visit would have a "limited" effect on the trade negotiations.
Xinhua also said that Kim and Xi agreed to make efforts for continuous "new development", a "political settlement process of the Korean Peninsula" and "more benefits" for the people of the two countries and that they would contribute to peace and stability, prosperity and development of the region and beyond.
Ties between China and North Korea, which had frayed as Pyongyang stepped up its missile and nuclear tests up to late 2017, warmed over the past year as Kim engaged with China, South Korea and the United States.