Sixteen people, including eight primary school children, were injured in a mass stabbing outside Tokyo on Tuesday morning local time, national broadcaster NHK reported.
Two children and an adult were without vital signs after the attack in Kawasaki city, southwest of central Tokyo, NHK said, citing police.
A suspect was detained on the spot and was badly hurt after stabbing himself in the shoulder, NHK said.
It said the man, likely in his 40s to 50s, began slashing at people waiting at a bus stop. Two knives, along with some victims, were found in a nearby park, according to NHK.
Violent crime is rare in Japan but there have periodically been high-profile attacks that have shocked the nation.
A stabbing spree on a school bus and a commuter bus in a Tokyo suburb in 2010 injured more than a dozen people.
Two years earlier, a 28-year-old man drove a truck into a crowded pedestrian crossing in Tokyo, killing three people, and then fatally stabbed four more.