North Korean leader Kim Jong Un has sent his "warmest congratulations" to Chinese President Xi Jinping on securing a third term as head of China's ruling Communist Party, state media reported Sunday.

The unusually prompt report from Pyongyang's official Korean Central News Agency came after the Chinese Communist Party's Central Committee elected Xi as its general secretary for another five-year term.

"Please accept my warmest congratulations to you upon the glad news that... you were elected again as the general secretary of the Party Central Committee," read Kim's message carried by KCNA.

"I, together with you, will shape more beautiful future of the DPRK-China relations meeting the demand of the times," Kim said, using the acronym of the North's official name.

China is North Korea's longtime ally and economic benefactor, their relationship forged in the bloodshed of the Korean War, when Mao Zedong sent millions of "volunteers" to fight US-led United Nations forces.

Ties have fluctuated over the years due to Pyongyang's growing nuclear ambitions, but the two have been working to repair their relationship.

Xi, 69, was also reappointed head of China's Central Military Commission, keeping him in charge of the People's Liberation Army.

• Xi secures historic third term as China's leader

He is now all but certain to sail through to a third term as the country's president, due to be formally announced during the Chinese government's annual legislative sessions in March.

Sunday's developments cement him as the most powerful Chinese leader since Communist Party founder Mao Zedong.