North Korea fired dozens of artillery shells onto a South Korean island on Tuesday, killing one person and triggering an exchange of fire as southern armed forces went on their highest state of alert.
In what appeared to be one of the most serious border incidents since the 1950-53 war, South Korean troops fired back with cannon, the government convened in an underground war room, and "multiple" air force jets scrambled.
The firing came after North Korea's disclosure of an apparently operational uranium enrichment programme — a second potential way of building a nuclear bomb — which is causing serious alarm for the United States and its allies.
Some 50 North Korean shells landed on the South Korean border island of Yeonpyeong near the tense Yellow Sea border, damaging dozens of houses and sending plumes of thick smoke into the air, YTN television reported.
One South Korean marine — part of a contingent based permanently on Yeonpyeong — was killed and 13 other marines were wounded, the military said. YTN said two civilians were also hurt.
"A North Korean artillery unit staged an illegal firing provocation at 2:34 pm (0534 GMT) and South Korean troops fired back immediately in self-defence," a ministry spokesman told AFP.
"A Class-A military alert issued for battle situations has been imposed immediately," the spokesman said.
One island resident, Lee Jong-Sik, told YTN: "At least 10 houses are burning. I can't see clearly for the smoke. The hillsides are also on fire.
"We were told by loudspeakers to flee our homes."
Another resident recounted a "thunderous sound outside".
"When I walked out, the whole village was on fire," the villager was quoted by Yonhap news agency as saying. "I'm at the evacuation site with other villagers and I am scared to death."
Yeonpyeong lies just south of the border declared by United Nations forces after the inconclusive war six decades ago, but north of the sea border declared by Pyongyang.
The Yellow Sea border was the scene of deadly naval clashes in 1999, 2002 and last November.
Tensions have been acute since the sinking of a South Korean warship in March, which Seoul says was the result of a North Korean torpedo attack. Pyongyang has angrily rejected the charge.
In late October, North and South Korean troops exchanged gunfire across their cold war border, stoking tensions in the buildup to the G-20 summit of world leaders in Seoul earlier this month.