North Korea has launched three short-range missiles and all three have dropped into the sea, says South Korea's defence ministry.
Presidential spokesperson said Seoul does not consider the missile launch a serious security threat.
The ministry said North Korea launched the missiles off its eastern coast. Two missiles had been detected by South Korea in the morning. They were followed by a third one later in the day.
"A more detailed analysis will be needed but the missiles launched may be a modified anti-ship missile or the KN-02 surface-to-surface missile derived from the Soviet era SS-21 that has a range of about 120 km," said a South Korean defence ministry official.
The missiles were probably aimed at South Korean waters, said authorities.
According to Seoul's Yonhap, the authorities are uncertain whether it was an attack or part of a military exercise.
North Korea had earlier deployed two medium-range missiles targeting US bases in the region, but they were later withdrawn.
All the ministries in Seoul have been on high alert, and developments in North Korea are being closely monitored.
"All information has been shared real time between the presidential office and the defence ministry. The situation is being monitored carefully," said presidential spokesman Kim Haing.