North Korea's neighbors, US President Donald Trump and the United Nations welcomed Friday's historic inter-Korean summit, while urging progress towards denuclearisation.

At the first summit between the Koreas in more than a decade, North Korean leader Kim Jong Un and his South Korean counterpart, Moon Jae-in, pledged to work for the "complete denuclearisation of the Korean peninsula".

The two sides said they would work with the United States and China to declare an official end to the 1950-1953 Korean War and seek an agreement to establish "permanent" and "solid" peace in place of an armistice.

Trump welcomed the talks while injecting some caution.

"After a furious year of missile launches and Nuclear testing, a historic meeting between North and South Korea is now taking place. Good things are happening, but only time will tell!" he said on Twitter.

Trump, who traded personal insults and threats with Kim in the past year over Pyongyang's development of nuclear-armed missiles capable of hitting the United States, said he looked forward to meeting the North Korean leader in coming weeks with the aim of completely denuclearising the Korean peninsula.

Trump also praised Chinese President Xi Jinping, who backed tough UN sanctions that further isolated impoverished North Korea and squeezed its economy.

China, which is North Korea's main ally and is wary of being sidelined amid the thaw between the rival Koreas and the upcoming summit between Trump and Kim, said it was willing to continue playing a role in resolving the decades-long standoff between the rival Koreas over the North's nuclear and missile programs.

WATCH: North and South Korea pledge to get rid of their nuclear weapons

Kim made a dramatic surprise visit last month to Beijing, where he met with Xi.

China "hopes all relevant sides can maintain the momentum for dialogue and work together to promote the denuclearisation of the peninsula and the process for the political settlement of the peninsula issue," China's Foreign Ministry said in a statement.

"China is willing to continue playing a proactive role in this regard," it added.

Japanese Prime Minister Shinzo Abe said he "strongly" hoped Pyongyang would take concrete steps to carry out its promises to pursue denuclearisation. "I will keep a close watch on North Korea's future conduct," Abe told reporters.

Asked if he was concerned that Japan might be left out of the denuclearization process, Abe said, "Absolutely not. I talked with President Trump for more than 11 hours just a while ago and reached a complete agreement on our action, effort and basic policy."

In Moscow, the Kremlin called the summit very positive news and said President Vladimir Putin had long advocated direct talks between the two countries.

Asked about the prospect of Trump also meeting the North Korean leader, Kremlin spokesman Dmitry Peskov told reporters Moscow welcomed any steps that would ease tensions.

South Korean President Moon Jae-in and North Korean leader Kim Jong Un raise their hands at the truce village of Panmunjom. Photo: Reuters

China, Russia, Japan and the United States, along with the two Koreas, took part in on-off six-party talks on North Korea's nuclear program. The talks stalled in 2008.

United Nations Secretary-General Antonio Guterres called the summit "truly historic" and said he counted on both sides to build on their first meeting and swiftly implement all agreed actions and make "progress towards sustainable peace and verifiable denuclearisation on the Korean Peninsula."

"He looks forward to these gains being consolidated and advanced at the summit between the leaders of the United States and (North Korea) expected to take place in the near future," a UN statement added.

Britain's foreign minister, Boris Johnson, welcomed the positive developments but said North Korea must now honour its commitments and take concrete steps to denuclearise.