During a two-day trip, his first visit to North Korea in seven years, Xi is to meet leader Kim Jong-un.
It will be their first summit since September, when they met in Beijing after viewing a military parade alongside Russian President Vladimir Putin and other foreign leaders.
China's official Xinhua news agency reported that Xi had arrived in Pyongyang, after earlier reporting that Xi's entourage includes his wife Peng Liyuan and top officials including Foreign Minister Wang Yi and top Communist Party official Cai Qi.
No specific agenda has been mentioned.
Foreign experts predict the meeting will have big ramifications on bilateral ties and beyond, as they both seek to fully restore their traditional alliance in the face of separate confrontations with the US.
"A Chinese leader doesn't just visit North Korea because a visit is due. Xi's trip will have real implications for China-DPRK relations," said Leif-Eric Easley, a professor at Ewha University in Seoul, using the abbreviation for North Korea's full name.
Sway over North Korea could help Xi's dealings with US
Xi's trip comes after his back-to-back summits with US President Donald Trump and Putin in Beijing last month. Xi is expected to meet Trump again on a planned US visit in September.
Xi will try to demonstrate China's "sway over the Korean Peninsula" and "a leadership role in entire Northeast Asia in the ages of strategic competitions with the US," said Kwak Gil Sup, the head of One Korea Center, a website specialising in North Korea affairs.
China has long been North Korea's economic lifeline and main diplomatic backer. Experts say China has avoided fully enforcing UN sanctions on North Korea and sent clandestine aid to help its impoverished neighbour stay afloat.
This year marks 65 years since the two countries signed a mutual defence treaty.
But there have been questions about their ties in recent years, with North Korea prioritising co-operation with Russia by supplying troops and weapons to support its war against Ukraine. In return, North Korea has received economic and military assistance from Russia.
Restoring an exclusive influence over North Korea would give Xi a leverage in dealings with Trump, who has repeatedly expressed his desire to restart diplomacy with Kim, experts say.
Xi would likely offer Kim economic aid packages such as shipments of rice and fertilisers, a resumption of Chinese group tourism to North Korea. and joint economic projects, analysts said.
"North Korea can't solely rely on Russia. It needs to align with China," Kwak said.
In a Monday editorial, the Rodong Sinmun newspaper called Xi "the most honoured state guest," saying Pyongyang's streets "are filled with an atmosphere of friendship".
Xi could also refrain from pressing Kim on the issue of denuclearisation of North Korea, and vaguely speak about peace and stability on the Korean Peninsula. That would be essential for Kim, who is desperate to win international recognition as a nuclear weapons state as a way to call for lifting of UN sanctions on North Korea.
