SEOUL (AFP) – North Korea fired dozens of artillery shells onto a South Korean island on Tuesday, killing one person, setting homes ablaze and triggering an exchange of fire as the South’s military went on top 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 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 the frontline island — was killed and 13 other marines were wounded, the military said. YTN said two civilians were also hurt.

“A Class-A military alert issued for battle situations was imposed immediately after shelling began,” a military spokesman said.

Sporadic firing by each side continued for over an hour before dying out, the military said.