North Korean leader Kim Jong-un has sent a personal letter to President Moon Jae-in to express his support for South Korea to overcome the outbreak of the new coronavirus, Cheong Wa Dae said Thursday.

In the letter, delivered to Moon on Wednesday, Chairman Kim consoled South Koreans fighting the virus and wished for their good health, according to Yoon Do-han, Cheong Wa Dae's senior secretary for public communication.

"The North's leader said he will quietly support South Korea's fight against COVID-19 and showed his constant friendship and trust toward Moon," Yoon said, adding that Kim expressed concerns about Moon's health.

In return, Moon sent a letter to his North Korean counterpart, expressing his gratitude.

Kim also revealed his "frank" thoughts about situations on the Korean Peninsula, but Cheong Wa Dae did not elaborate.

The two leaders' rare exchange of letters came as South Korea has reported 6,088 confirmed cases since the outbreak started on Jan. 20.

North Korea has not reported any confirmed infections, but it has intensified preventive efforts by tightening its border with China, where the virus originated, and toughening quarantine procedures for foreigners.

Kim's message came just one day after Kim Yo-jong, sister of the North's leader, issued a rare statement late Tuesday night that condemned Cheong Wa Dae for voicing its "strong concern" about her country's latest rocket-artillery drills.

On Monday, the North fired two projectiles into the East Sea.

Pyongyang described them as "long-range artillery pieces," which Seoul views as de facto short-range ballistic missiles.

The two Koreas' ties remain frayed, apparently due to North Korea's complaint about slow progress over the resumption of inter-Korean projects amid the international sanctions regime.

In a speech to mark the March 1 Independence Movement Day, Moon proposed cooperation with North Korea in the health care sector in response to the spread of the new coronavirus. Pyongyang has not been responsive to Moon's overture.

North Korea's nuclear talks with the United States have stalled due to the gap between the two sides over the scope of sanctions relief and the definition of denuclearization.

This marks the first exchange of letters between Moon and Kim this year.

In October 2019, Kim sent a condolence message over the death of Moon's mother, and Moon sent a personal letter to invite Kim to South Korea's special summit with ASEAN held in the southeastern port city of Busan in November last year. (Yonhap)