It came amid indications of possible preparations by Pyongyang for resuming high-profile provocations like test-firing a long-range rocket.

With regard to the recent stalemate in the Korea peace process, Xi was quoted as telling Moon, "There are many people worrying about the tense situation on the Korean Peninsula."

Xi stressed that "China and South Korea should join forces in making North Korea and the United States maintain the dialogue momentum," according to a Cheong Wa Dae spokesperson.

He went on to say that the two regional powers can "achieve a lot of things if they join hands," emphasizing that these were his "genuine words," Ko told reporters in an in-flight briefing as South Korea's Air Force One headed to the southwestern city of Chengdu.

Xi said there has been "more common ground" between the two sides on the Korean Peninsula issue since Moon's inauguration in May 2017.

"The joint position of the both nations to realize the denuclearization of the Korean Peninsula has become a strong basis for their cooperation," Xi was quoted as adding in the summit held in the Great Hall of the People

Moon agreed: "Maintaining North Korea-US dialogue momentum is more important than any other thing."

They also talked about a draft of a fresh UN Security Council resolution, proposed by China and Russia, calling for some of the sanctions in place against the North to be eased, Ko said.

Satellite images reportedly showed increased activities in the secretive communist nation's long-range rocket launch site near its border with China, coupled with its stated threat of a "Christmas gift" for the Trump administration, apparently referring to a major provocation.

Pyongyang has set a year-end deadline for Washington to change tack and put forward a fresh offer based on a "new calculation" in nuclear bargaining.

The North announced Sunday it has decided to bolster its military capability during the latest meeting of the Central Military Commission of the Workers' Party presided over by leader Kim Jong-un.

Meeting each other for the first time in six months, Moon and Xi were scheduled to have half-hour talks but the summit lasted 55 minutes. They also had a working lunch together.

On the trade war between Beijing and Washington, Xi said his government plans to handle it "with flexibility," Ko said.

"Cooperation would lead to interest for everybody, while a fight leaves scars on all of us," Xi was quoted as saying.

In response, Moon expressed hope that Beijing and Washington will resolve the problem through "constructive dialogue" and welcomed their recent "phase one" deal.

Xi again called on Moon to "appropriately" resolve the issue of an advanced US missile defense system named THAAD stationed in South Korea, and Moon explained his government's position.

On the cross-border spread of fine dust, Moon and Xi agreed that this kind of environmental issue is directly associated with the health and quality of life of people in both nations.

Moon invited Xi to visit Seoul as early as possible, saying it would serve as another chance to deepen the Seoul-Beijing "strategic cooperative relationship," and Xi said he would "actively consider" it.

China's Xinhua news agency reported that Xi called for joint efforts to elevate bilateral ties to a higher level.

"The two countries should further tap the potential and lift the level and standard of pragmatic cooperation to realize high-quality and integrated development," Xi told Moon, according to an English-language Xinhua report.

A Cheong Wa Dae official said the two leaders had "candid discussions" on a wide range of issues.

The official refused to confirm, however, whether they discussed the sensitive issue of South Korea hosting new ground-launched, intermediate-range missiles, the possibility of which has been a subject of speculation.

Shortly after landing in Chengdu, meanwhile, Moon had separate talks with Chinese Premier Li Keqiang, who is to host this year's trilateral summit, set to begin Tuesday and also involving Japanese Prime Minister Shinzo Abe.

Moon and Li agreed to facilitate talks on supplementing a bilateral free trade agreement (FTA) in the service and investment sectors, Cheong Wa Dae said. The FTA took effect in late 2015 and the two sides have been seeking to expand it.

On Tuesday afternoon, Moon plans to have one-on-one talks with Abe, which may serve as a chance to improve relations between two neighboring countries that have been embroiled in a trade fight for months, apparently over a dispute about shared history.

In what is viewed as a conciliatory gesture ahead of the Moon-Abe summit, the Japanese government said last week it has relaxed some export restrictions against South Korea.

The measure affects only photoresist, a chemical used to make semiconductors and one of three products subject to tightened customs procedures.

Moon's office, Cheong Wa Dae, said the move constitutes "some progress" but emphasized it is not sufficient to resolve the export control problem.

Moon and Abe's previous bilateral summit talks were in September last year, when they traveled to New York for a United Nations General Assembly session. (Yonhap)