Sixteen other girls between the ages of 6 and 12 and a woman were wounded by the man, who appeared to be in his 50s and died later of a self-inflicted wound, broadcaster NHK said on Tuesday, citing police.

Police said an 11-year-old girl and a 39-year-old man were killed, but declined to give further details. The 39-year-old was believed to be the father of one of the girls, NHK said.

The motive for the attack was not clear but there were no immediate fears of a wider security threat. There have been previous examples of mass stabbings in Japan, sometimes involving vulnerable targets.

The girls were students at a private Catholic school in Kawasaki city south of Tokyo and were boarding their school bus when the suspect attacked, according to NHK.

The Asahi newspaper quoted a witness saying he saw a middle-aged man with knives shouting "I'll kill you!" and about eight children lying on the ground around him.

The suspect, a resident of Kawasaki, was found unconscious at the scene and died later from a self-inflicted stab wound to his neck, NHK reported, citing police.

Prime Minister Shinzo Abe described the attack as "extremely harrowing" and promised to step up efforts to secure the safety of children commuting to and from school.

A witness told NHK he saw people lying on the ground covered in blood and one police officer was hosing down the sidewalk.

Violent crime is relatively rare in Japan but occasional high-profile incidents have shocked the nation.

In 2016, a knife-wielding man broke into a facility for the disabled in a small town near Tokyo and killed 19 patients in their sleep.

Australian Associated Press