North Korea has fired four ballistic missiles, three of which landed in Japan's Exclusive Economic Zone, Japanese Prime Minister Shinzo Abe said.
The move comes as South Korea and the United States are holding their joint military exercises, which Pyongyang sees as preparations for an invasion.
Kwon Ki-joon, a spokesman for the South Korea Defense Ministry spokesman, said "several projectiles" flew about 1,000 kilometers (620 miles).
The firing took place in Tongchang-ri, in the country's North Pyongan province, and the projectiles are believed to have landed in the Sea of Japan, which is also known as the East Sea, according to a South Korean Defense Ministry official.
South Korean President Hwang Kyo-ahn is scheduled to chair a meeting of the country's National Security Council at 9 a.m. local time.
Foal Eagle
The firing comes as South Korea and the United States are holding their annual military exercises, known as Foal Eagle, which both countries say are defensive in nature.
North Korea has already denounced this year's exercises through state media service KCNA.
"Now that the US imperialists and the South Korean puppet forces again kicked off the dangerous nuclear war drills against the DPRK at its doorstep, our army will counter them with the toughest counteractions," it said.
The exercises usually draw condemnation and retribution from Pyongyang.
During last year's drills, North Korea fired multiple short to medium range missiles and announced it could place nuclear warheads on its weapons.
The firing also comes a day after Seoul quadrupled the award for North Korean defectors and nearly a month after North Korea test-fired a new type of missile, the Pukguksong-2, a medium-long range ballistic missile.
That missile was also fired from North Pyongan province and traveled 500 kilometers (310 miles) before landing in the Sea of Japan.
The launch happened while Japanese Prime Minister Shinzo Abe was in the United States visiting US President Donald Trump.
North Korean state media reported that Kim Jong Un personally oversaw the operation.
But perhaps the biggest story coming from the Kim family recently has been they mystery surrounding the death of the the North Korean leader's eldest half-brother, Kim Jong Nam.
He died February 13 -- shortly after the Pukguksong-2 launch -- in Kuala Lumpur while en route to Macau.