North Korea apparently fired rockets from a multiple rocket launcher towards the open sea, according to the South Korean military on Sunday.
It was therefore initially unclear how far the alleged rockets flew.
The South Korean armed forces are still on standby and monitoring the situation, the general staff said.
Since the beginning of the year, the self-declared nuclear power North Korea has repeatedly tested missiles that can carry a nuclear warhead, in violation of UN resolutions.
The South Korean news agency Yonhap reported, citing military officials, that North Korea apparently fired four shots from a multiple rocket launcher towards the Yellow Sea within an hour on Sunday morning.
The National Security Council in Seoul held an emergency vice minister-level meeting.
According to reports in the South Korean media, a spokeswoman for the Office of the President spoke of "short-range projectiles".
North Korea also conducted two missile tests in late February and early March, which the United States and South Korea believe are related to Pyongyang's work on a new type of ICBM.
North Korea itself spoke of important tests in the development of an earth observation satellite.
Despite a ban by the United Nations, the country has been developing rockets of different ranges, which can also carry a nuclear warhead, for years.