North Korea fired around 200 artillery shells off its west coast which fell into water early Friday, according to South Korean military.
According to Seoul's Joint Chiefs of Staff, the shells "splashed into the maritime buffer zone north of the Northern Limit Line," which is the de facto maritime border, Seoul-based Yonhap News reported.
Pyongyang is yet to make a statement about its latest military activities.
South Korean authorities meanwhile ordered its residents of Yeonpyeong Island, facing North Korea in waters off its eastern coast, to evacuate to shelters.
The military said it "detected the artillery firings from Jangsan Cape, north of South Korea's northernmost island of Baengnyeong, and Deungsan Cape, north of the South's western border island of Yeonpyeong, from 9 a.m. (0300GMT) to 11 a.m. (0500GMT)."
An official on Yeonpyeong Island said: "We announced the evacuation after receiving a call from a military unit saying it was carrying out a maritime strike on Yeonpyeong Island as it has a situation with a North Korean provocation."
The maritime buffer zone between two Koreas was set under now-defunct inter-Korean military accord which was signed on Sept. 19, 2018.
Seoul had partially suspended the pact, aimed at reducing border tensions, before North completely scrapped it last November.
South Korea's move came after North Korea successfully launched, in its third attempt last year, a military satellite.
Meanwhile, North Korea is reportedly rebuilding guard posts in concrete inside the demilitarized zone, which separates the two Koreas.
The two sides had demolished at least 10 guard posts each inside the zone following the 2018 military pact.
Pyongyang's launch of artillery shells also comes after South Korea assumed a two-year seat at the UN Security Council since this Monday.
