In the one of the most serious flare ups since the Korean War of the early 1950s, North and South Korea have exchanged artillery fire. At least two South Korean marines were killed and several others, and some civilians, were injured after North Korea shelled a small South Korean island.
The shelling prompted South Korea to scramble fighter jets. It set off the highest peace-time alert level here, sending top government leaders into an underground war room for emergency talks.
South Korea's government calls the act a clear military provocation and unpardonable.
Presidential press secretary Hong Sang-pyo says Pyongyang must take responsibility. Additional provocations by North Korea will compel South Korea's military to forcefully retaliate, he says.
Army General Lee Hong-Ki terms the attack an inhumane atrocity. The general says the shelling clearly violates the United Nations armistice.
In Pyongyang, the evening TV newscast put the blame on South Korea, saying North Korea only fired after it repeatedly warned South Korea to halt military maneuvers on the island.
The announcer, quoting a North Korean Army statement, warns if South Korea intrudes into its territorial waters "even 0.001 millimeters" its forces will not hesitate to continue taking "merciless military counter-actions."
The United States, which has 25,000 troops in South Korea, condemned the attack, saying that North Korea must halt belligerent action and abide by the 1953 armistice.
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.