US President Donald Trump, who has agreed to meet with Kim Jong Un, said today there is a now a good chance the North Korean leader will give up his country's nuclear weapons.

"For years and through many administrations, everyone said that peace and the denuclearization of the Korean Peninsula was not even a small possibility," Trump wrote in an early morning tweet.

"Now there is a good chance that Kim Jong Un will do what is right for his people and for humanity. Look forward to our meeting!," Trump added.

His comments came as Kim completed a secretive and unprecedented visit to Beijing on Wednesday as the two countries seek to repair frayed ties before Pyongyang's landmark summits with Washington and earlier with South Korea.

On his first trip abroad since taking power, Kim and his wife were greeted by an honor guard and a banquet hosted by President Xi Jinping, according to state media, which confirmed the three-day visit on Wednesday only after Kim had returned by train to North Korea.

The two men held talks at the Great Hall of the People and Kim pledged he was "committed to denuclearization" on the Korean peninsula, according to China's Xinhua news agency.

Kim also expressed willingness to hold the summits with Trump and South Korean President Moon Jae-in, it said.

Analysts said Xi likely wanted to see Kim in order to ensure North Korea does not cut a deal with Trump that hurts Chinese interests during their summit, expected to be held in May.