South Korea's Joint Chiefs of Staff said several missiles lifted off from North Korea's eastern coastal Wonsan area on Wednesday morning and flew about 240km towards the North's eastern waters.
It said an additional North Korean ballistic missile fired later on Wednesday travelled more than 700km off the North's east coast.
South Korea's military said it maintained a readiness to repel any provocations by North Korea under a solid military alliance with the United States.
It earlier said it detected the launch of an unidentified projectile from North Korea's capital region on Tuesday.
South Korean media reported the projectile, also likely a ballistic missile, disappeared from South Korean military radars after displaying an abnormal development in the initial launch stage.
This indicated the launch ended in failure, according to the reports.
The back-to-back launches came after North Korea made it clear that it had no intentions of improving ties with South Korea, whose liberal government has steadfastly expressed its hopes to restore long-dormant dialogue.
On Tuesday night, Jang Kum-chol, first vice-minister at Pyongyang's foreign ministry, said South Korea would always remain North Korea's "most hostile enemy state".
He derided South Korea as "world-startling fools" engaged in wishful thinking over a recent statement by Kim Yo-jong, the influential sister of North Korean leader Kim Jong-un.
After South Korean President Lee Jae-myung expressed regret over alleged civilian drone flights into North Korea, Kim Yo-jong late on Monday praised him for what she called honesty and courage, but reiterated a threat to retaliate if such flights recurred.
South Korean officials responded by describing Kim Yo-jong's statement as meaningful progress in relations.
Jang said her statement was intended as a warning.
He cited Kim Yo-jong as calling South Korea "the dogs affected by mange that blindly bark to the tune of neighbouring dogs" as she criticised it for recently co-sponsoring of a UN resolution on the North's purported human rights violations.
North Korea has refused to return to talks with South Korea and the U.S. and pushed to expand its nuclear arsenal since Kim Jong-un's diplomacy with US President Donald Trump collapsed in 2019.
North Korea has instead sought to strengthen ties with Russia, China and other countries embroiled in confrontations with the US.
