"We on both sides consistently agree to continue to realise the denuclearisation of the Korean peninsula and firmly protect peace and stability on the peninsula," Xi said during a joint appearance with South Korea's President Park Geun-Hye.
Park arrived in Beijing today for summit talks to be dominated by Pyongyang's nuclear programme, seeking to push China to do more to bring its wayward ally North Korea to heel.
China has previously supported denuclearisation but tended to prioritise regional stability, for decades acting as the sole major ally and economic lifeline to the unpredictable North.
Washington and Seoul have made it clear they will never accept the idea of North Korea as a nuclear state, and insist Pyongyang must show a tangible commitment to abandoning its nuclear weapons if it wants substantive talks.
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Both have pressured China to use more of its leverage to rein in Pyongyang.
While a planned meeting with South Korea fell through, it has offered direct talks with Washington, and has sent two envoys to Beijing in the past four weeks.
China's relationship with North Korea -- famously described by Mao Zedong as being as close as "lips and teeth" -- was forged in the 1950-53 Korean War which China entered to prevent the North's total defeat.
But it has weakened significantly over the years, as China's economic transformation has distanced it from the ideological rigidity of the dynastic Kim regime across the border.
In line with UN sanctions, Beijing has moved to restrict Pyongyang's financial operations in China which the international community says are the major conduit for funding its nuclear weapons programme.
During Park's visit, Beijing will also seek to strengthen the overall strategic relationship with Seoul, said Peking University professor of international relations Jia Qingguo.
Today, the two sides signed eight agreements in various fields including energy, trade, technology and oceanic cooperation.