China, Russia and Japan quickly expressed concern and appealed for calm on the Korean peninsula.

South Korea's military says its forces fired back with 80 shells after tiny Yeonpyeong island, 12 kilometers off the North Korean coast, was hit.

Residents on Yeonpyeong say damage is widespread.

Fishing boat captain Shin Eung-ho says a shell fell next door, but he was not home at the time. He says the island was hit by an initial barrage of 15 shells, then there was a break of 40 minutes before the shelling resumed, setting afire and destroying many homes.

Video showing plumes of dark smoke rising from the island were repeatedly shown on South Korean news.

Yeonpyeong has more than 1,000 residents, some of whom headed into bunkers. Others began fleeing in boats.

The maritime boundary nearby is disputed, and the area saw deadly clashes at sea in 1999 and 2002.

The two Koreas have remained technically at war since 1953. Their three-year civil war ended in stalemate and no peace treaty was signed.