One missile was test-fired from the eastern city of Wonsan at 5:20 a.m., the South Korea Joint Chiefs of Staff (JCS) said.
"Our military has maintained readiness as (we are) bracing for possibilities of additional provocations," said Jeon Ha-gyu, the chief of public affairs for the JCS.
It appears to be the latest in a string of missile tests as the country tries to advance its weapons program in defiance of the international community and its closest regional ally, China.
Initial reports suggested it was an intermediate-range Musudan missile, according to a U.S. defense official; if confirmed, it would be the fourth time North Korea has tried and failed to launch this type of missile.
The missile apparently flew for about two or three seconds and then exploded, the official said. It's not clear if the missile made it over water.
China's Ministry of Foreign Affairs urged all parties "to refrain from taking any action that may escalate tensions" on the Korean Peninsula.
Yoshihide Suga, Japan's chief cabinet secretary, said that no missile was confirmed to have flown towards Japan.
The last several months have been particularly contentious on the Korean Peninsula, after North Korea claimed to have tested its first hydrogen bomb
and fired a satellite into orbit. Both actions violated numerous United Nations Security Council resolutions.
Earlier this month, North Korean leader Kim Jong Un proposed holding military talks with South Korea
to ease tensions but Seoul dismissed the offer, saying it wasn't sincere given that Pyongyang was continuing to develop a nuclear arsenal.
U.S. President Barack Obama, speaking at the G7 summit in Japan on Thursday, said that North Korea was a "big worry."
"They're not at the point right now where they can effectively hit U.S. targets, but each time that they test, even if those tests fail, they learn something," he said.
"It's clear that ideologically they're still convinced that -- and Kim Jong Un in particular seems to be convinced that his own legitimacy is tied up in the developing of nuclear weapons."