(CNN) -- North Korea fired 30 short-range rockets into the sea off the eastern coast of the Korean peninsula early Saturday, a South Korean defense ministry official said.
The rockets have an estimated range of 60 km (37 miles), according to the ministry.
North Korean officials did not send out a navigational warning to ships before the apparent test, the official said.
It marks the fourth known rocket test by Pyongyang this month. The country fired 25 short-range rockets into the water earlier this week.
The launches have drawn criticism from South Korea and the United States as provocations by the North.
The U.S. and South Korea have been conducting a joint annual military drill since February, and North Korea has said its missile tests are a justifiable defensive reaction to them.