Four of the victims were stabbed, with the others injured as they fled the scene, Kyodo News agency reported, citing police.
Over 14 people, including a 16-year-old girl, were injured in the attacks, local fire department spokesman Toshio Iyoka said.
The attacker boarded two buses during the attack, Kyodo said. The victims included seven high school students and four middle school students, according to reports.
The attacks occurred in front of Toride Station, in Ibaraki Prefecture, about 25 miles northeast of Tokyo.
A man was arrested for attempted murder after the attacks, according to local police spokesman Toru Ueki.
The incident evoked memories of an attack in central Tokyo in 2008. In that attack, which drew national attention for its ferocity, a man slammed a truck into a crowd of people in the Akihabara electronics district and began stabbing passers-by at random.