North Korea fired at least two more ballistic missiles on Thursday, one of them sailing over northern Japan and landing in the Pacific Ocean, according to Japanese and South Korean officials.
Warnings were issued for residents in the Japanese prefectures of Miyagi, Yamagata and Niigata to shelter in their homes or go underground.
The latest barrage comes a day after North Korea fired at least 23 missiles on Wednesday, one of which landed off South Korea's coast and forced a populated South Korean island to evacuate.
Wednesday's launches marked the most missiles North Korea has ever fired in a single day, according to South Korea.
Pyongyang also fired more than 100 rounds of artillery on Wednesday into a buffer zone established in a 2018 military agreement with South Korea.
"Our military can never tolerate this kind of North Korea's provocative act, and will strictly and firmly respond under close South Korea-U.S. cooperation," South Korea's Joint Chiefs of Staff said on Wednesday.
It comes as the U.S. and South Korea conduct "Vigilant Storm," which involves more than 200 warplanes.
The Associated Press contributed to this report.