Pyongyang's fourth launch in a week comes amid a flurry of military muscle-flexing by countries in the region, including joint anti-submarine exercises on Friday by the navies of South Korea, the United States and Japan, Reuters reported.
The rival Koreas are in a regional arms race that has seen a major increase of weapons and military spending.
Marking South Korea's 74th Armed Forces Day, South Korean President Yoon Suk-yeol condemned what he called recent military provocations by the North and vowed to strengthen joint military drills with the United States.
He and military officials observed a major show of advanced weaponry, including multiple rocket launchers, ballistic missiles, main battle tanks, drones and F-35 fighter aircraft, among other systems.
The U.S. military demonstrated fighter jets and attack aircraft. Images of the event showed Yoon saluting from the back of a convertible car while driving by rows of tanks and other weapons.
Saturday's two short-range missiles were launched from Sunan, north of the capital Pyongyang, South Korea's Joint Chiefs of Staff said in a statement. It estimated the range at 350 km (220 miles) at 30 km (20 miles) altitude and speed of Mach 6.
Japan's coast guard reported at least two suspected ballistic missile tests by Pyongyang. The missiles flew 400 km and 350 km, reaching an altitude of 50 km, said Defence Minister Toshiro Ino.
Tokyo has lodged a protest against the North through diplomatic channels, Ino said, adding the missiles possibly flew an "irregular trajectory" designed to evade missile defence.
U.S. Vice President Kamala Harris visited the region this week, meeting with Yoon in Seoul on Thursday.
North Korea fired missiles before and after Harris' visit to South Korea, extending a record pace in weapons testing this year as it increases the threat of a credible nuclear power that can strike the United States and its allies.
Pyongyang also conducted the first intercontinental ballistic missile test since 2017.