South Korea said it is working with the US to analyze the specifications of the missiles.
North Korea fired cruise missiles toward the western waters on Saturday following an earlier threat to use nuclear arms over the arrival of a US nuclear-capable submarine in South Korea.
South Korea detected several launches from around 4 a.m. and is working with the US to analyze the specifications of the missiles, its Joint Chiefs of Staff said in a text message.
The launches follow a warning from North Korean Defense Minister Kang Sun Nam earlier this week that the dispatch of the USS Kentucky puts Pyongyang within its rights to use a nuclear arm.
US Deputy Pentagon press secretary Sabrina Singh slammed North Korea for the threat, calling it "dangerous" and saying that the port call is a sign of long-standing cooperation with South Korea. Seoul has also denied the deployment is a demonstration of nuclear weapons to Pyongyang.
Washington is separately seeking the release of a US soldier who crossed into North Korea on foot on Tuesday. The two countries have no direct diplomatic ties.