At least 16 people, including children, were injured on Tuesday in a stabbing attack in the city of Kawasaki, south of Tokyo, the local fire department said.
"A man stabbed them," Dai Nagase, spokesman for the Kawasaki Fire Department, told AFP.
"We received an emergency call at 7.44am, which said four elementary schoolchildren were stabbed."
Police said one suspect, a man, had been detained.
Public broadcaster NHK said he had stabbed himself, suffering a serious wound.
The broadcaster said two knives were spotted at the scene, but there was no immediate confirmation from officials.
The attack occurred at a park not far from a local train station, local media said.
Footage broadcast on local TV stations showed multiple police cars, ambulances and fire engines at the scene.
Emergency medical tents were put up to treat the wounded.
Two children and an adult were without vital signs after the suspected stabbing in Kawasaki city, west of Tokyo, NHK said, citing city authorities.
