South Korea's defense report says the weapon would make possible a large-scale surprise attack on Seoul, the capital, and the surrounding areas, NHK reported.
The Rodong Sinmun reported on Wednesday that leader Kim Jong Un oversaw the test-firing of 240 millimeter-caliber shells on Tuesday.
The report says the rocket shells have a newly applied guidance system and enhanced destructive power. The report included an image of a shell purportedly accurately hitting a target.
The newspaper notes that Kim set forth an important policy to be pursued in producing the new artillery pieces and equipping army units with them. Kim previously said that deployments would be completed by 2026.
The report says the system is in production at defense industrial enterprises under the Second Economic Commission that oversees the defense industry.
Observers say the test-firing shows Pyongyang's stance to counter the United States and South Korea, which are conducting a joint military exercise through Thursday.