Xi was replying to Kim's congratulatory message last week on his re-election as the leader of the ruling Communist Party of China (CPC) at the 19th Congress of the party. Xi will remain in power at least until 2022.
"I wish that under the new situation, the Chinese side will make joint efforts with the North Korean side to promote the sustainable soundness and stable development of the relations between the two nations," Xi was quoted as saying by the Korean Central News Agency (KCNA).
The Chinese leader cited the need for "defending regional peace, stability and common prosperity," it added.
The reported exchange of cordial messages came amid a widespread view that China's ties with its longtime ally are not like before Kim took power in late 2011. Xi and Kim have not held summit talks yet.
China, seeking to play a "responsible" role in the international community, is apparently annoyed by repeated provocations by the recalcitrant neighbor.
Beijing has shown some indications of toughening sanctions on Pyongyang for its latest nuclear test in September.
Emboldened by the start of another five-year term as China's leader, Xi appears to be reaching out to neighboring countries.
On Tuesday, China announced an agreement with South Korea to end their yearlong row over the deployment of the THAAD missile defense system here.BY YONHAP