The Democratic People's Republic of Korea (DPRK) appears Friday to have fired about 20 artillery shells, South Korea's Joint Chiefs of Staff (JCS) said.

South Korean military detected sounds of artillery fire around the South Korean island of Yeonpyeong near the disputed sea border called Northern Limit Line (NLL) off the west coast of the Korean peninsula, starting about 7:50 a.m. (2250 GMT) through 11:50 a.m. (0450 GMT), the JCS told Xinhua.

Friday's alleged shooting comes after the DPRK for the last two days fired artillery shells into waters north of the NLL, within the range of no-sail zones the country recently designated until Friday.

The move is also defiant of South Korean military's warning Wednesday to stop "provocative" acts and cancel its designation of no-sail areas which South Korea said includes its waters.

Seoul's military has thus far shown muted response by firing warning shots into the air in response to the first round of shooting from the DPRK on Wednesday, but it is considering deploying artillery-locating radars and additional self-propelled howitzers in Baekryeong and Yeonpyeong Islands in the Yellow Sea, near the disputed maritime border, according to local media.

The contentious sea border, a constant source of tension between the two Koreas where the latest naval skirmish took place in November last year, was fixed unilaterally by the U.S.-led United Nations Command after the 1950-953 Korean War.