North Korean leader Kim Jong-un is on a trip to China for talks with Chinese President Xi Jinping, state media reported Tuesday, raising speculation that his second summit with US President Donald Trump might be forthcoming.

Kim and his wife, Ri Sol-ju, left for China on Monday afternoon for a four-day visit at the invitation of the Chinese president, Pyongyang's Korean Central News Agency said. China's Xinhua news agency also confirmed his visit.

Last year, Kim traveled to China and met with Xi three times before and after he held his first-ever summit with Trump in June in Singapore.

In the Singapore summit, Kim agreed to work toward complete denuclearization of the Korean Peninsula in exchange for security guarantees and new relations with the US.

Progress, however, has been slow in denuclearization for months as the North calls for sanctions relief, while Washington says such concessions would not be granted until the North completely gives up its nuclear weapons.

In his New Year's speech last week, the North's leader warned that he could take a new way if the US clings to pressure and sanctions on its regime. He still kept the door open for talks with the US, saying he is willing to meet Trump at any time.

He also called for multilateral talks involving the signatories to the truce that ended the 1950-53 Korean War, including China, and replacing it with a peace treaty. The issue could be discussed during his trip to China this week, observers said.

Trump earlier said that the US and North Korea are in talks over where to hold their second summit, adding that the decision on the venue will be announced in the "not-too-distant future."

Experts see Kim's trip to China might be intended to demonstrate to the world that their relations remain strong and also reflect the North's push to project its image as a normal state.

"It is rare that the North's leader travels overseas at the start of the year. (His trip to China) shows how important it is to advance relations between the North and China," Yang Moo-jin, a professor at the University of North Korean Studies, said.

"It is also aimed at showing off the image of a leader of a normal state," he added.

Xi is expected to visit North Korea soon as the two countries mark the 70th anniversary of establishing diplomatic ties this year.

Experts say that Kim's trip to China could be followed by his visit of Seoul or meeting with US President Trump as early as February.

Kim agreed to travel to Seoul for the first time as a North Korean leader "at an early date" during his summit meeting with South Korean President Moon Jae-in in September.

In a personal letter to Moon last month, he expressed disappointment for not making a trip to Seoul by the year's end and hoped to fulfill his promise soon. (Yonhap)