South Korea says that North Korea has launched eight short-range ballistic missiles eastward toward the sea in about 30 minutes shortly after 9:00 a.m.
The South Korean military is analyzing information in close cooperation with the US military.
The two countries just concluded a three-day joint drill on Saturday. It was the first in 4 years and 7 months that they used a nuclear powered aircraft carrier in a joint drill.
The missile launch is believed to be a part of North Korea's reaction to the drills as well as to the close collaboration of the US, Japan and South Korea.
The US and South Korea agreed to enhance deterrence capabilities including US nuclear weapons at their summit in May.
The US and Japan's leaders expressed shared serious concerns to the North's nuclear and missile issues during their summit meeting in Tokyo last month. They confirmed stronger collaboration.
North Korea has launched missiles with exceptional frequency this year. Launches have occurred in every month so far.