The Joint Chiefs of Staff (JCS) said the projectiles were fired at 2.59 a.m. and 3.23 a.m. from Yonghung, South Hamgyong Province, into the East Sea, reports Yonhap News Agency.
Both projectiles flew around 220 km at an altitude of about 25 km, according to the JCS, adding that they flew at a top speed of Mach 6.9.
What the North fired appears to be a new type of short-range ballistic missiles, but more analysis is needed, the presidential office Cheong Wa Dae said.
Earlier in the day, American media also reported, citing US officials, that North Korea fired two short-range ballistic missiles Friday.
"We are monitoring the situation in case of additional launches and maintaining a readiness posture," the JCS said.
In Washington, a senior US official said he is aware of the North's latest launches.
"We are aware of public reports of additional missile launches from North Korea today," the official told Yonhap News Agency.
"We continue to monitor the situation and are consulting closely with our South Korean and Japanese allies."
Last week, North Korea test-fired two short-range ballistic missiles off its east coast, saying it sent a "solemn" warning to South Korea over its planned military exercises with the US this month.
On Wednesday, North Korea fired two more such missiles, according to the JCS. Pyongyang disputed the assessment, saying it had tested a new rocket launch system.
The UN Security Council resolutions ban North Korea from launching ballistic missiles of any kind.
( With inputs from IANS )