Update (1800 EST): North Korean ground based rocket systems fired retaliatory shots 90 minutes after South Korean naval vessels evicted a Northern merchant vessel. While the North is threatening a larger response, the two navies do not seem to actively be engaged in combat, like in 2009 and 2002.
South and North Korean vessels are currently exchanging fire at the Northern Limit Line near Baengnyeong Island. 30 minutes ago a North Korean merchant vessel, Mupo, crossed into South Korean waters and was given several warning shots by a South Korean military vessel.
The North Korean have just threatened retaliation by “firing 10 missiles” at South Korean vessels “invading” the West Sea.