SEOUL North Korean artillery fired at least one shot which landed near a South Korean navy patrol ship south of the two sides' disputed maritime border on Thursday, but it did not hit the vessel, a military official in Seoul said.
The official added that South Korean artillery fired at a North Korean naval vessel in response.
Residents of the Yeonpyeong island, which lies just south of the disputed sea border, were evacuated to bomb shelters, the official said, speaking on condition of anonymity. Shelling by North Korean artillery killed four people on the island in 2010.
There was no further firing from the North following the incident soon after 6 p.m. local time (0900 GMT), the official said.
North Korea has refused to recognize the so-called Northern Limit Line that was drawn up at the end of the 1950-53 Korean War and has frequently challenged it with intrusions of ships or more recently by firing artillery near or across the line.
Earlier on Thursday, North Korea had issued its latest threat to "blow up" any South Korean warships, in an angry response to an incident earlier in the week when the South fired warning shots at the North's patrol boats that breached the line.
The North accused South of "a grave provocation" at the time and said its vessels were merely trying to contain Chinese fishing boats that were in the area illegally.
Also, earlier on Thursday, the South's Defense Ministry spokesman Kim Min-seok said North Korea had no business interfering in operations of South Korean naval vessels south of the Northern Limit Line.
In March, the North fired more than 500 rounds of artillery in an exercise, but 100 rounds landed south of the border, prompting the South to fire more than 300 shots back.
The Northern Limit Line, a maritime border that wraps itself around a part of the North's coastline, has been the scene of frequent clashes.
Earlier in 2010, a South Korean naval vessel was sunk close to the line by what an international commission said was a North Korean torpedo, although the North denies involvement.
The two sides are still technically at war as the conflict ended in a mere truce, not a treaty.
(Additional reporting by Choonsik Yoo; Editing by Simon Cameron-Moore)