South Korean marines conducted live-fire artillery drills on the border island of Yeonpyeong, the Yonhap news agency reported, hours after North Korea staged an artillery barrage in the area.
The troops held "live-fire artillery drills with K9 self-propelled howitzers," Yonhap said, the first such drills in the area since both countries dropped a military accord in November.
Earlier, North Korea had fired more than 200 artillery rounds into the sea near the tensely defended maritime border with South Korea, a military official said, while residents of two South Korean islands were ordered to evacuate due to an unknown "situation".
South Korea's defence ministry said that the North Korean artillery barrage near two border islands was a "provocative act" and urged it to stop, warning the South Korean government would take "appropriate measures" in response.
"This is a provocative act that threatens the peace on the Korean Peninsula," the defence ministry said in a statement, urging North Korea to "immediately cease these actions" and warning they would take "appropriate measures in response".
An official on Yeonpyeong island, which sits just south of the disputed Northern Limit Line (NLL) sea border, said the evacuation was ordered at the request of the South Korean military.
The firing by North Korea caused no civilian or military damage in the South, South Korea's military said in a news briefing.
"This is an act of provocation that escalates tension and threatens peace on the Korean peninsula," a spokesman for the South Korean Joint Chiefs of Staff said.
Residents of Baengnyeong island, which lies far to the west of Yeonpyeong and also near the sea border, were also told to evacuate, a village official there said.
In 2010, North Korean artillery fired scores of rounds at Yeonpyeong island, killing four people, including two civilians, in one of the heaviest attacks on its neighbour since the Korean War ended in 1953.
North Korea said at the time it was provoked into the attack by South Korean live-fire drills that dropped shells into its territorial waters.
China calls for restraint from all sides
Meanwhile, China has called for "restraint" from all sides.
"Under the current situation, we hope that all relevant parties maintain calm and restraint, refrain from taking actions that aggravate tensions, avoid further escalation of the situation, and create conditions for the resumption of meaningful dialogue," foreign ministry spokesman Wang Wenbin told reporters.
"We are paying close attention to developments and changes to the situation on the Korean Peninsula," Mr Wang added.
"Confrontations between relevant parties have intensified recently, and the situation on the peninsula continues to be tense.
"As a neighbour of the peninsula, China has always advocated maintaining peace and stability on the peninsula and resolving peninsula issues through dialogue and consultation."
