The South Korean military had previously been active on the border.
The North Korean military opened artillery fire towards the sea as a warning to Seoul. This was reported by the South Korean news agency Yonhap.
It is reported that the General Staff of the Korean People's Army gave such an order in response to the South Korean military. Earlier they had shown activity near the border. It happened at 09:15 (local time) on Tuesday, December 6.
Pyongyang appealed to Seoul to stop the provocation.
The shelling came a day after North Korea fired 130 artillery shells from multiple rocket launchers into the maritime buffer zone in response to a joint U.S.-South Korean exercise near the border.
Seoul said the DPRK army's actions contradicted the inter-Korean military agreement. It was concluded in 2018 and aims to reduce tensions in areas near the border.