A knife-wielding attacker killed a 12-year-old schoolgirl and a man before stabbing himself to death in a rampage outside Tokyo Tuesday that also injured more than a dozen, including several children.

The mass stabbing in the town of Kawasaki, south of the Japanese capital, was a rare attack in a country with one of the lowest rates of violent crime in the developed world, and there was no immediate detail on the suspect's motive.

Kiyoshi Matsuda, deputy director of the Nippon Medical School Musashi Kosugi Hospital, told reporters that the 12-year-old schoolgirl and a 39-year-old man had succumbed to their injuries.

Local media reported that the suspected attacker, a man in his 50s, had also died of his wounds after turning the knife on himself. Emergency services said at least 16 others had been injured in the attack.

"It is a very harrowing case. I feel strong anger," Japan's Prime Minister Shinzo Abe said in televised remarks.

"I offer my heartfelt condolences to the victims and hope the injured recover quickly."

According to local media, eyewitnesses saw a middle-aged man clasping a knife near the bus stop where the children were waiting, shouting "I will kill you."

A local man living nearby, who identified himself as Matsumoto, 25, said he went outside after hearing screams.

"It's hard to describe what it was like, how it sounded. It wasn't girls having fun, it was a sound that was absolutely not normal," he told AFP.

"I saw a man lying on the street. I also saw a girl hunched over on the ground. There were also five or six girls, maybe they were the ones who screamed... There was blood all over them."

The attack occurred during the busy early morning commute as workers headed to their offices and children to school. Fire department officials said they received the first emergency calls shortly before 8:00 am local time.

The scene of the attack was still swarming with emergency personnel hours later, with three police vans parked around the spot to block it from view.

Emergency workers set up an orange medical tent to treat the wounded, and ambulances and fire engines were parked nearby.

A white school bus with blue stripes was parked at the site, with the name "Caritas Gakuen [school]" written on the side, said an AFP correspondent at the scene.

The bloodshed came as US President  Donald Trump wrapped up a state visit to Japan, and offered his "prayers and sympathy" to the victims as he met troops outside Tokyo.

Standing aboard a Japanese military ship, he said that "all Americans stand with the people of Japan and grieve for the victims and for their families."