, Two shells fell near the South Korean ship, which was sailing near the front-line island of Yeonpyeong, the South’s defence ministry said.
“North Korea fired shells which fell near our ship, but it did not cause any damage to our ship,” a ministry spokesman told AFP.
The North’s move began at 6:00 pm (0900 GMT), prompting a response from the South Korean vessel which fired several rounds into North Korean territorial waters, he said.
The North’s military threatened Wednesday to attack South Korean warships “without any warning” if there was even a “trifle” violation of the maritime border.
The threat came a day after a South Korean naval ship fired warning shots to stop an incursion by three North Korean patrol boats across the sea
The South’s navy urged the North to stop “absurd threats” and warned: “We will mercilessly punish any provocative actions by North Korea”.
The North does not recognise the Yellow Sea border, the scene of brief but bloody naval clashes in 1999, 2002 and 2009.
In addition, in November 2010, North Korea shelled Yeonpyeong island, killing four South Koreans and briefly triggering concerns of a full-scale conflict.
In March the North fired hundreds of shells in a live exercise near the sea boundary. About 100 shells dropped into South Korean territorial waters, and the South responded with volleys of shells into North Korean waters.
Cross border tension has been high for months, amid signs that the nuclear-armed North may be preparing to conduct a fourth atomic test.
This month the two Koreas have upped the rhetorical ante in their verbal exchanges over crashed surveillance drones recovered on the South Korean side of the border.
Seoul said a joint investigation with US analysts had provided “smoking gun” evidence that the drones came from the North. Pyongyang flatly denied its involvement.