"It is the unshakable will of our party and people to further consolidate and develop generation after generation the traditional DPRK-China friendship, which stood all tests of history, from a long-term and strategic viewpoint despite the complicated international situation," Kim said in the message.
DPRK stands for the North's official name, the Democratic People's Republic of Korea.
"I am convinced that the invincible vitality of the DPRK-China friendship, a common treasure of the peoples of the two countries, will be more strikingly demonstrated in the future thanks to the common efforts of both sides," the message said, according to Pyongyang's official Korean Central News Agency.
China is Pyongyang's No. 1 ally and a key provider of economic aid and diplomatic protection.
In recent months, however, China has apparently been taking a tougher approach to Pyongyang, especially after the North's long-range rocket launch in December and its third nuclear test in February. Beijing has since backed a U.N. sanctions resolution against the North and has been carrying out the restrictions more vigorously than before.