Artillery fire was exchanged between the two Koreas on Monday afternoon.
In the midst of live-fire drills, a North Korean artillery shell landed south of the inter-Korean maritime border.
The South Korean military responded by firing back across Northern Limit Line.
For the details, let's go live to our correspondent Hwang Sung-hee at the Arirang News Center.
Sung-hee, what's the latest?
The exchange of fire between the two Koreas came to an end about two hours ago.
South Korea's Joint Chiefs of Staff says it all began at a little past noon on Monday when North Korea fired hundreds of artillery shells in waters north of the Northern Limit Line.
Several of those shells fell south of the NLL in South Korean waters near Baengnyeong Island.
A spokesperson for the Joint Chiefs of Staff said the South Korean military shot around 50 artillery shells back across the NLL in response using K-9 self-propelled howitzers.
Residents of South Korea's border island were told to take cover in shelters.
North Korea had notified South Korea of its plans to conduct live-fire drills this morning, announcing they would carry out exercises in seven West Sea border regions, north of the NLL.
It had not given a specific time for the planned exercise, but demanded that Seoul keep its vessels out of the training zone.
How is the South Korean military now preparing for the event of another incident?
South Korea's defense ministry took the unusual warning from its neighbor this morning as a hostile threat.
This is the first time in recent history that the North has conducted a live-fire drill in all seven West Sea border regions.
It's also the first time it's informed the South of the exercise ahead of time.
During a press briefing this morning, the vice defense ministry spokesman had said South Korea will keep close watch for possible clashes, as they believe the North is attempting to raise tensions near the western maritime border.
The South Korean military has activated crisis management operations and has deployed naval convoys near the NLL to cope with any contingencies.
Officials in Seoul have been on high alert, and it's worth mentioning that this is not the first time the North has fired artillery shells this direction.
In 2010, North Korea launched artillery strikes on a South Korean border island, killing four.
Thank you for your report, Sung-hee.
That was Arirang News' Hwang Sung-hee with the latest on North Korea's live fire drills.