The South Korean Joint Chiefs of Staff said that one ballistic missile flew a distance of 800 kilometers overland toward the sea off the country's east coast, while a second projectile, assumed to be a missile, was detected by radar but disappeared at an altitude of about 17 kilometers.
The military said it was closely tracking and monitoring the situation and maintaining a readiness posture for any North Korean provocation.
U.S. official confirmed the launch, with a U.S. defense official telling CNN that it tracked two ballistic missiles.
The launch came around 5:55 a.m. local time, near Sukchon county, South Pyongan province, the Joint Chiefs of Staff said.
It comes one week after North Korea fired two missiles from North Hwanghae province, south of Pyongyang, toward the sea east of the Korean Peninsula.
Japan's Prime Minister Shinzo Abe condemned North Korea's actions and called on the country "to exercise self-restraint." He said Japan would take "precautionary measures," including surveillance.
The action is the latest display of military power on a peninsula that roils with tension.
Last week's launch appeared to be confirmed in a report from the state-run Korean Central News Agency. It followed a North Korean claim that it had miniaturized nuclear warheads to fit on ballistic missiles
, according to KCNA.
The agency published a statement that "all agreements on economic cooperation and business exchanges adopted by North and South are invalid."
And Seoul last month ordered the closure of the Kaesong industrial complex
, a rare symbol of cooperation between the two Koreas.
Describing the shuttering of Kaesong as a "unilateral" move, KCNA said Pyongyang "will completely liquidate all South Korean companies and relevant assets" within its borders.
Seoul has condemned the suspension of economic ties, with the Unification Ministry saying it would "never accept" the move, which it described as a "provocative action."
The statement added it would hold Pyongyang responsible for any damage to South Korean assets north of the border.
Tensions have heightened on the Korean Peninsula since a fourth North Korean nuclear test
and joint U.S.-South Korean military drills.
Around 17,000 U.S. military personnel and 300,000 South Korean troops are taking part in what the South Korean Defense Ministry described as the "largest ever" joint military exercises.
North Korea has warned that it would make a "pre-emptive and offensive nuclear strike
" in response to the joint exercises.
While Pyongyang often issues saber-rattling statements during annual U.S. and South Korean joint exercises, the anger level has increased this year, according to Mike Chinoy, a former CNN senior international correspondent and the author of "Meltdown: The inside story of the North Korean nuclear crisis
Pyongyang's claims that it has miniaturized nuclear warheads comes after the North reported a successful test of what it said was a hydrogen bomb in January.