South Korea has said it is stepping up security and surveillance across the country in view of possible provocations from North Korea hours after a confrontation in the tense border region.
South Korean's defence ministry said it would "sternly respond" to any aggressive move by North Korea amid rising tensions between the rivals.
"The South Korean and U.S. forces have stepped up their surveillance and vigilance with increased military assets in all parts of the nation to prepare for possible provocations. If North Korea uses the live-fire drill as an excuse to launch provocations near South Korean islands and shores, we will sternly respond," defence ministry spokesperson Kim Min-seok told reporters in Seoul.
Inhabitants in the border islands have been told to evacuate to alternative shelters.
The spokesperson said Pyongyang's forces had fired more than 500 rounds of artillery shells during the earlier confrontation that took place in the disputed maritime bordering region, which South Korea calls as Northern Limit Line (NLL).
After 100 rounds of the shells fell in the South Korean territory, Seoul's forces responded by firing nearly 300 rounds.
"We believe the North's maritime firing is a planned provocation and an attempt to test our military's determination to defend the Northern Limit Line and to get an upper hand in South-North relations," the spokesperson said.
Fighter jets have also been deployed near the border, he added.
Meanwhile, China has expressed concern over the situation and urged both sides to show restraint.
Beijing's foreign ministry spokesperson Hong Lei told reporters: "Currently, there has been a rising tension on the Korean Peninsula, and we have concerns about this. We hope the relevant parties will exercise restraint, refrain from taking actions that may escalate tensions and make joint efforts to uphold peace and stability on the Korean Peninsula."