The train carrying Kim Jong Un, the top leader of the Democratic People's Republic of Korea (DPRK), left Vietnam from the train station in the border town of Dong Dang on Saturday, starting his long journey home through China.

Kim arrived in Hanoi for his second summit with U.S. President Donald Trump on Tuesday, after a three-day, 4,500-km journey from Pyongyang to Dong Dang via train. Then he paid an official two-day visit to Vietnam on Friday and Saturday.

His meeting with U.S. President Donald Trump was, however, cut short after they failed to reach a deal. But the two leaders agreed to continue "productive" discussions on denuclearization, according to Pyongyang's state media.

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Chinese State Councilor and Foreign Minister Wang Yi urged patience in the U.S.-DPRK talks with DPRK Vice Foreign Minister Ri Kil Song in Beijing shortly after the summit.

Commenting on the summit, Wang said their talks have entered a "deep-water zone" and it is inevitable that difficulties would emerge in one way or another. 

He underscored China's optimism in the prospect of talks and commitment to playing a constructive role in issues on the peninsula.

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Before leaving Hanoi, Kim laid wreaths at Vietnam's war memorial and Ho Chi Minh Mausoleum.

During his official visit in Vietnam, Kim met with Vietnamese Prime Minister Nguyen Phu Trong.

The two sides agreed to facilitate high-level visits, and expand the exchange of all-level delegations via the party, state and mass organization channels, according to Vietnam News Agency.

He also met with Vietnamese Prime Minister Nguyen Xuan Phuc and top legislator Nguyen Thi Kim Ngan on Friday.