Kim Jong-un is visiting Beijing at Chinese President Xi Jinping's invitation as he prepares for a second summit with US President Donald Trump.
North Korean leader Kim Jong-un and Chinese President Xi Jinping have discussed an expected US-North Korea summit in talks in Beijing, Yonhap news agency says.
It comes days after Kim warned he may take an alternative path if the US does not ease sanctions.
Kim's visit to China, confirmed by North Korean and Chinese state media, comes amid plans for a second summit with US President Donald Trump aimed at denuclearising the Korean peninsula.
South Korea's Yonhap, without identifying its sources, said the two leaders held talks for an hour on Tuesday in which they discussed the second US-North Korea summit and strengthening bilateral ties.
The meeting was followed by a dinner hosted by Xi and his wife, Yonhap said.
Kim held three summits last year with Xi, his most important ally, before and after summits with Trump and South Korean President Moon Jae-in.
Kim and Trump pledged to work towards denuclearisation at their landmark June summit in Singapore, but the agreement was short on specifics. Negotiations have made little headway since.
"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 the US-based Centre for the National Interest, said in an emailed statement.
"In fact, during his New Year's Day speech, Kim's 'new way' that he referred to may well have been a veiled threat to move closer to Beijing. That should make America quite concerned."
Kim left for China on a private train on Monday afternoon accompanied by his wife, Ri Sol Ju, and senior North Korean officials, including Kim Yong Chol, a key negotiator in talks with the US, and foreign minister Ri Yong Ho, North Korea's state-run KCNA news agency said.
China's official Xinhua news agency confirmed that Kim was visiting from Monday to Thursday at Xi's invitation.
The visit coincides with what South Korean officials say is Kim's 35th birthday on Tuesday.
Kim's visit to North Korea's most important economic and diplomatic ally follows reports of advanced negotiations for a second summit between Washington and Pyongyang aimed at resolving the standoff over North Korea's nuclear and missile programs.
Kim said in his New Year speech he was ready to meet Trump any time to achieve their common goal of denuclearisation of the Korean peninsula. But he warned that he may seek an alternative path if US sanctions and pressure against the country continued.