China will play a "constructive" role in resolving tensions on the Korean peninsula, Beijing's top envoy to Pyongyang said Tuesday.

Beijing is Pyongyang's most important ally and economic benefactor, their relationship forged in the bloodshed of the Korean War in the 1950s.

China's special representative on Korean peninsula affairs, Liu Xiaoming, is in Seoul this week for his first visit to the South since taking office. He met his South Korean counterpart, Noh Kyu-duk, on Tuesday.

The two envoys discussed the "grave situation" on the Korean peninsula and measures for "stable management", Seoul's foreign ministry said.

Liu expressed "the Chinese side's willingness to play a constructive role for the peaceful resolution of the Korean peninsula issue", the ministry added in a statement.

North Korea has carried out more than a dozen weapons tests this year, including launching its most powerful missile since 2017.

Pyongyang had paused long-range and nuclear tests while leader Kim Jong Un met then-US president Donald Trump for a bout of doomed diplomacy, which collapsed in 2019. Talks have since stalled.

Analysts warn of further missile tests, likely timed around the inauguration of South Korea's new president next week or US President Joe Biden's visit to the country later this month.

Recent signs of new activity at North Korea's key nuclear testing site have also raised concerns over a possible resumption of nuclear tests.

North Korea is reeling economically from a self-imposed coronavirus blockade, and only restarted cross-border trade with Beijing earlier this year.

China accounts for more than 90 percent of the isolated country's trade.

Pyongyang is under multiple sets of international sanctions over its nuclear and ballistic missile programmes.