Kim Jong-un travels to China in secretive visit for talks with Xi Jinping

North Korean leader uses his official plane to make the short flight to Dalian, in what was his first international flight since assuming power

North Korean leader Kim Jong-un visited China and met President Xi Jinping in a secret trip this week revealed by the state media of both countries; their second encounter in two months amid warming ties between the Cold War allies.

Talks in the northeastern coastal city of Dalian come as tension on the Korean peninsula over North Korea's development of nuclear weapons eases ahead of what would be a historic meeting between Mr Kim and US President Donald Trump, as soon as this month, according to the White House.

China has been keen to show it has an indispensable role to play in seeking a lasting solution to tension over North Korea, concerned that its interests may be ignored, especially as North Korea and the United States establish contacts.

Mr Kim, during his visit on Monday and Tuesday, told Mr Xi he hoped relevant parties would take "phased" and "synchronised" measures to realise de-nuclearisation and lasting peace on the Korean peninsula.

"So long as relevant parties eliminate hostile policies and security threats towards North Korea, North Korea has no need for nuclear (capacity), and de-nuclearisation can be realised," China's official Xinhua news agency cited Mr Kim as saying.

He told his Chinese counterpart that the de-nuclearisation of the peninsula was North Korea's "constant and clear position", and that dialogue between North Korea and the United States could build mutual trust.

Chinese state media showed pictures of Mr Kim smiling in an outdoors meeting with Mr Xi, and the two leaders strolling along a waterfront.

Mr Xi hosted a banquet and told Mr Kim of his backing of North Korea's "strategic shift towards economic development", Xinhua added.

"China supports North Korea's upholding of de-nuclearisation on the peninsula, and supports North Korea and the United States resolving the peninsula issue through dialogue and consultation," Mr Xi said.

North Korean state media said Mr Kim was "very pleased" that the relationship with China was reaching a high point, and North Korea would cooperate with China more actively as the situation on the Korean peninsula changed.

The visit, part of a flurry of diplomatic engagement that has dramatically eased tension, follows Mr Kim's recent historic summit with South Korean counterpart Moon Jae-in.

It also followed Mr Kim's dramatic train journey to Beijing in March, his first known trip abroad since assuming power in 2011.

Mr Trump said on Twitter that he would speak with Mr Xi by telephone on Tuesday morning in Washington, calling the Chinese leader "my friend".

"The primary topics will be trade, where good things will happen, and North Korea, where relationships and trust are building," Mr Trump said.

Mr Kim used his official aircraft to make the short flight to Dalian, in what was his first international flight since assuming power.

A passenger plane reportedly used for North Korean high-ranking officials takes off from an airport in Dalian after Mr Kim's meeting with his Chinese counterpart (Kyodo News via AP)

His father, Kim Jong Il, feared flying, fuelling speculation that the younger Kim may not be willing to travel far to meet Mr Trump. The venue for their summit has not been announced.

The demilitarised zone, or DMZ, between North and South Korea, and Singapore are believed to be the most likely contenders for the venue.

South Korea's presidential office said the Chinese government notified Seoul about the Xi-Kim meeting in advance.

"The Chinese government informed that Kim had arrived in Dalian on Monday and returned to Pyongyang today. It was a one-night-two-days stay," the office said.

Intense secrecy typically surrounds high-level North Korean visits to China, and this week's unannounced trip was no different.

Throughout the day on Tuesday there was speculation on Chinese websites that a North Korean leader was in China, though China's foreign ministry said earlier it had no information and Chinese state media did not carry any reports.

Japanese public broadcaster NHK had shown images of two North Korean aircraft taxiing at Dalian's airport, one an Air Koryo plane and another carrying a North Korean emblem, although the North's state airline does not have regular flights to the Chinese city.

Posts about unusual traffic jams and security in Dalian popped up on Chinese social media.

China is North Korea's most important economic and diplomatic backer, despite its anger over its repeated nuclear and missile tests. China has supported tough UN sanctions against the North.

But the two sides have stepped up engagement since Trump surprised the world in March by saying he would be willing to meet Mr Kim, signalling the possibility of a major breakthrough in nuclear tensions with North Korea.

Reuters