Chinese President Xi Jinping on Sunday told his North Korean counterpart Kim Jong Un that Beijing hoped to "deepen friendly... cooperation" with Pyongyang, as the two leaders exchanged messages to mark a major diplomatic anniversary.

China and North Korea are traditional socialist allies, and Beijing has long provided crucial support for Pyongyang's diplomatically isolated government.

State media in both countries said Xi and Kim exchanged congratulatory messages on Sunday to mark the 75th anniversary of the establishment of diplomatic relations.

"China is willing to work with the North Korean side... to strengthen strategic communication and coordination, deepen friendly exchanges and cooperation, (and) write a new chapter in the traditional bilateral friendship," Xi said, according to state news agency Xinhua.

He added that Beijing and Pyongyang "have worked closely to promote regional peace and stability, and uphold international fairness and justice", Xinhua reported.

North Korean state news agency KCNA reported that Kim said Pyongyang "will steadily strive to consolidate and develop the friendly and cooperative relations between (North Korea) and China".

China and North Korea have stepped up diplomacy since ending years-long border restrictions imposed during the Covid-19 pandemic.

Analysts say Pyongyang relies heavily on Chinese firms and banks to skirt international sanctions and buttress its military and moribund economy.

Bilateral ties have seemingly become more complex in recent months as North Korea has drawn closer to its other main ally Russia, with Kim announcing support for President Vladimir Putin's ongoing invasion of Ukraine.