China's vice foreign minister is visiting North Korea, the ministry said Monday, making him Beijing's most senior envoy known to go to Pyongyang since its young leader executed his uncle, a key China interlocutor.

The late Jang Song-Thaek was North Korea's second most powerful figure, and provided a valuable link between the two countries before being purged in December following a sidelining of other core leaders.

"Vice foreign minister Liu Zhenmin will start his visit to the DPRK from today and the visit will last until February the 20th," Beijing foreign ministry spokeswoman Hua Chunying said at a regular press briefing, referring to the North by its official name, the Democratic People's Republic of Korea.

She added that, "as far as I have learnt, it is a regular exchange of two foreign ministries".

Earlier this month, Hua said another Chinese foreign ministry delegation had visited Pyongyang, also casting it as a continuation of close communication between the two sides.

China is the North's key ally and protector, providing badly-needed trade and aid for fear that a collapse of the regime could unleash chaos across the border and allow the United States to bolster its presence in Asia.

Yet Pyongyang routinely defies Beijing's calls for calm, restraint and denuclearisation, pushing ahead with nuclear weapons tests and issuing apocalyptic threats against the US and South Korea.

Relations have been further strained since Kim Jong-Un took over power in the North after his father Kim Jong-Il died in 2011, making him the third leader in a family dynasty.

Washington often urges Beijing to put greater pressure on its neighbour, but from China's standpoint the US could wield greater leverage over the stubborn regime if it provided security assurances.