Japan's Kyodo news agency said earlier the assailant, Tomohiro Kato, 25, from the Shizuoka Prefecture, was arrested and had admitted to the attack.
The agency quoted Kato as telling investigators: "I came to Akihabara to kill people. I am tired of the world. Anyone would do. I came alone."
The Akihabara district is known for its numerous electronics stores, and as a focus of Japanese comic book and video game culture.
Police said the victims ranged in age from 19 to 74, but have not specified how many of them died from stab wounds, and how many from being hit by the truck.
An eyewitness interviewed on TV channel NHK said the attacker "was screaming as he was stabbing people at random."
Before the stabbing spree, which took place at around 12:30 p.m. local time (03:30 GMT), Kato ran over three people in a truck, NHK said.
