A top North Korean general and confidant of leader Kim Jong-Un met a senior Chinese official in Beijing Wednesday, with relations between the allies strained ahead of a China-US summit.

Choe Ryong-Hae, director of the Korean People's Army politburo, is a "special envoy" of the North's young leader, Pyongyang's official news agency said.

He met Wang Jiarui, head of the ruling Chinese Communist Party's International Department, said Beijing's foreign ministry spokesman Hong Lei, to "exchange views on the situation on the Korean peninsula and other issues of common interest".

Hong gave no details.

China is the North's sole major ally and chief economic benefactor. But the relationship has been sorely tested in recent months by Pyongyang's refusal to heed Beijing's warnings against provoking the international community with its nuclear and missile programme.

China has long been the North's main diplomatic protector. But it sided with the rest of the UN Security Council in imposing sanctions after the North's long-range rocket test last December and its nuclear test in February.

The measures triggered a dangerous cycle of escalating military tensions on the Korean peninsula, during which China came under enormous US-led pressure to rein in a wayward ally threatening nuclear strikes against the US and South Korea.

Choe is believed to be the highest-ranking North Korean party official to visit China since Kim's late father and predecessor Kim Jong-Il in August 2011.

Kim Jong-Un has not visited since taking power in December 2011 but sent his uncle Jang Song-Thaek, a powerful figure in the inner circle, to Beijing in August last year.

Northeast Asia expert Wang Dong of Peking University called Choe's trip a "somewhat encouraging sign" that Pyongyang might be open to talks, but warned it was still taking provocative steps such as firing short-range missiles.

"The question of course will be how serious North Korea will be," he said.

Yang Moo-Jin of Seoul's University of North Korean Studies said the timing was significant ahead of a June 7-8 summit between US President Barack Obama and China's new leader Xi Jinping.

And South Korea's new president Park Geun-Hye is expected to hold a summit with Xi in Beijing in late June.

"Choe is Kim Jong-Un's closest confidant, so Kim is sending his highest possible envoy to China ahead of the US summit," Yang told AFP.

"This will be Kim's way to deliver his message to Obama concerning peace on the Korean peninsula and the nuclear issue," he added.

Seoul and Washington have held out the prospect of talks with Pyongyang, but only if it shows a firm commitment to abandoning its nuclear weapons programme.

The North has made it clear its nuclear deterrent is not up for negotiation, but observers said Choe might be empowered to offer some assurances or concessions to China.

"He's Kim's top military guy, so clearly the North's nuclear and missile programme will be on the agenda," said Cheong Seong-Chang, an analyst at the Sejong Institute think-tank in Seoul.

"China is looking for some sign of compromise, and Choe might offer an assurance not to conduct any more nuclear tests for now," Cheong said, adding that the North might seek a Kim summit with Xi in exchange.

Cho Han-Bum of South's Korea Institute for National Unification said the North's "threats and military brinkmanship during the recent crisis didn't reap much in the way of reward, so Kim needs a boost and a China visit would help cement his legitimacy as leader".

The relationship between the two nations, forged in the 1950-53 Korean War, has weakened significantly over the years as China's economic transformation has distanced it from the ideological rigidity of the dynastic Kim regime.

In line with UN sanctions, Beijing has moved to restrict Pyongyang's financial operations in China which the international community says are the major conduit for funding its nuclear weapons programme.

The strain in relations was reflected most recently when a Chinese fishing boat with 16 crew was seized by unidentified North Koreans.

The detention caused outrage online in China, with Internet users calling on Beijing to take a tough stance against Pyongyang.