The reported launches Monday came three days after South Korea said the North fired a medium-range missile into the sea for the first time since early 2014.
Yonhap, citing an unidentified government source, said the South Korean military was trying to find what types of a missile and projectiles were fired.
South Korea's Defense Ministry said it was trying to confirm details.
The launches came as North Korea has condemned ongoing annual South Korean-U.S. military drills that it sees as an invasion rehearsal.
Related story
North Korea fires three projectiles into sea, South Korea says
