They were launched on Thursday morning local time (Wednesday evening GMT) from the city of Wonsan on North Korea's east coast, according to a statement from the joint chiefs of staff, carried by Yonhap news agency.
The statement described them as "a salvo of apparent ballistic missiles".
Under Kim Jong-un, there have been increasingly frequent North Korean tests, all of which defy UN sanctions.
South Korea's military said the missiles flew about 200 kilometres (125 miles).
North Korea has fired land-to-ship missiles, South Korea's military says.