Pyongyang has dramatically ramped up missile launches and military exercises in recent weeks, as Seoul and Washington say North Korean leader Kim Jong Un is close to conducting what would be his country's seventh nuclear test.

Roughly 100 artillery shells were fired from South Hwanghae province into the West Sea around 12:30 pm (GMT 0330) Wednesday, South Korea's Joint Chiefs of Staff (JCS) said, calling it a "clear violation" of the 2018 agreement.

"The North's continuing provocations not only undermine peace and security on the Korean peninsula but also for the international community. We strongly urge North Korea to immediately halt its actions," the JCS said in a statement.

It said none of the shells landed in South Korean waters south of the buffer zone.

Pyongyang on Wednesday said the latest barrage was intended to counter a "military provocation" by the South Korean army along the border earlier in the day.

"Enemies shot over 10 shells of multiple rocket launchers in the frontline zone off the foremost line occupied by the 5th Army Corps of the KPA between around 8:27 to 9:40 Wednesday morning," a spokesman for the General Staff of the Korean People's Army said in a statement carried by the official KCNA news agency.

"The enemies' successive military provocations in frontline areas must be stopped right now."

The latest barrage marked the North's second consecutive day of military provocation. It launched roughly 250 rounds into the maritime buffer zone off its east and west coasts on Tuesday.

Pyongyang earlier in the day said the Tuesday barrage was also in response to the "enemy's war drill against the North" along the border "as a powerful military countermeasure".

The North also fired artillery rounds into the military buffer zones last week.