A knife-wielding man went on the rampage yesterday in the city of Kawasaki, just outside Tokyo, stabbing to death an 11-year-old girl and a 39-year-old man.
At least 16 other people, mostly schoolgirls, were injured before the attacker died from a self-inflicted wound to the neck.
The two dead victims were identified as sixth-grader Hanako Kuribayashi and Mr Satoshi Oyama, who worked as a Burmese interpreter at the Ministry of Foreign Affairs. He was the father of a pupil who was unharmed in the incident which occurred just after 7.40am local time.
All the injured schoolgirls were waiting for their school bus to Caritas Elementary School.
Investigative sources told domestic media that Mr Oyama sustained wounds to his neck and back, likely in an attempt to protect other children from harm.
Police believe the attacker, 51-year-old Ryuichi Iwasaki, had targeted people at random. Two bloodied knives were reportedly recovered near the scene, while another two were found in his backpack. There was no immediate information on his motives.
According to eyewitness accounts, the man, who was bespectacled and had close-cropped hair, shouted "I'm going to kill you" as he went on the rampage.
He turned the knife on himself when a Caritas Elementary bus driver shouted at him, asking: "What are you doing?"
Rolling news footage throughout the day showed distinct pools of blood at the crime scene on a street near a park in a residential area close to Noborito train station.
Multiple police cars, ambulances and fire engines were at the scene, while emergency medical tents were erected to treat the injured.
The rampage sent shock waves throughout Japan, which has one of the lowest crime rates in the world, although it has also witnessed bouts of stabbings.
Prime Minister Shinzo Abe voiced strong anger about the harrowing attack, as he offered his condolences to the victims.
"The government must ensure children's safety by all means," Mr Abe said, convening an emergency meeting for today to discuss safety measures to protect elementary and junior high students on their commutes to and from school.
Yesterday's incident was the most severe stabbing involving primary school pupils since 2001, when then 37-year-old Mamoru Takuma entered Ikeda Elementary School in Osaka and began stabbing pupils and teachers at random.
Eight children died, while another 13 children and two teachers were severely wounded.
Mr Daisuke Fujita, chief of the National Mental Support Centre for School Crisis at Osaka Kyoiku University, told public broadcaster NHK that yesterday's rampage showed a need to consider how to better protect children going to and from school.
"Crime prevention measures have been improved in schools since the Ikeda incident," said Mr Fujita, who was principal of Ikeda Elementary from 2007 to 2011. "It is urgent to consider measures in areas where children gather, even if there is a limit to what can be done outside of school premises."
The director of Caritas' school operator Caritas Gakuen, Mr Tetsuro Saito, told a news conference: "The children did nothing wrong, while their parents whom so lovingly raised them are suffering so much. I feel extreme pain, to the point of not knowing what to do with my anger."
Meanwhile, in an apparently unrelated incident yesterday in Saitama city, north of Tokyo, police fired shots at a knife-wielding man in his 60s who had charged at them, hitting him in the abdomen.