Island authorities said many of the 8,700 residents on the five islands either stayed indoors or were escorted to bunkers and schools behind the hills that face North Korea, The New York Times reported.
North Korea's coastal artillery can reach the islands. In November 2010, one of the islands, Yeonpyeong, was attacked by artillery fire from North Korea, killing two marines and two civilians.
North Korea has claimed the waters around the five South Korean islands, which are patrolled by South Korean warships. In recent weeks, North Korea has criticized several joint military drills planned by South Korea and the United States.
The U.S. and South Korean armed forces are to being their major annual drill Feb. 27, the Times said. A joint air, ground and sea exercise is set for March 1-April 30.
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