The US military’s Pacific Command said it had detected three short-range ballistic missiles, fired over a 20-minute period.
The South Korean Office of the Joint Chiefs of Staff said the projectiles were launched from the eastern Kangwon province into the sea.
One appeared to have blown up almost immediately while two flew about 155 miles north-east.
The South Korean president’s office said the North may have fired an upgraded 300mm calibre multiple rocket launcher but military experts were still analysing the precise details.
Officials added that the missiles did not pose a threat to the US mainland or to the Pacific territory of Guam, which North Korea had threatened earlier this month to surround in a “sea of fire”.
North Korea’s official media reported on Saturday that Kim had guided a series of army strikes against targets modelled after South Korean islands.
The KCNA news agency quoted Kim as telling the army that it “should think of mercilessly wiping out the enemy with arms only and occupying Seoul at one go and the southern half of Korea”.
Tensions had eased since Pyongyang and Washington exchanged threats and the test came just days after senior US officials praised North Korea for not firing any missiles since late July.
Secretary of State Rex Tillerson had hoped that the lack of launches or other “provocative acts” by Pyongyang could mean a path could be opening for dialogue “in the near future.”
North Korea’s last test on July 28 was an intercontinental ballistic missile designed to fly 6,200 miles that would put parts of the US mainland within reach.
At the time President Donald Trump responded: “North Korea best not make any more threats to the United States.
“They will be met with fire and fury like the world has never seen. They will be met with fire, fury and frankly power the likes of which this world has never seen before.”
The White House said Mr Trump had been briefed about the latest missiles.