Seoul: North Korea test-fired three short-range ballistic missiles toward the Sea of Japan on Saturday, South Korea's Yonhap news agency reported.

The missiles were launched from Chunghwa County in North Korea's North Hwanghae Province at around 8 am local time on Saturday, Yonhap said, citing the South Korean Joint Chiefs of Staff (JCS).

"While strengthening our monitoring and vigilance, our military is maintaining a full readiness posture in close cooperation with the United States," the JCS said in a Saturday message, as quoted by Yonhap.

The Japanese Kyodo news agency said citing Japan's Defense Ministry that the three ballistic missiles flew over a distance of 350 kilometers (217 miles), reaching a maximum altitude of 100 kilometers. All of the missiles landed outside of Japan's exclusive economic zone.

Earlier on Saturday, Yonhap reported that Pyongyang test-fired one ballistic missile toward the Sea of Japan.

Japanese Prime Minister Fumio Kishida has instructed his government to conduct a detailed analysis of Saturday's test launch.

According to Japanese media reports, a crisis response centre has been set up under the Japanese prime minister's office. There has been no information on any damages.

Tokyo has expressed protest to Pyongyang over the Saturday test-firing, Kyodo reported.

North Korea has conducted nearly 40 test launches this year, firing around 70 missiles, including an intercontinental ballistic missile test-fired in November.

The latest test-firing carried out by Pyongyang on Saturday came after South Korea successfully test-fired a solid-fuel carrier rocket on Friday, as part of its efforts to strengthen space-based reconnaissance capabilities, according to South Korea's Defense Ministry.

According to CNN, North Korea has fired more than 90 cruise and ballistic missiles so far this year, showing off a range of weapons as experts warn of a potential nuclear test on the horizon.