Pictured: The knifeman who said 'I came to kill' as he stabbed seven shoppers in a busy Tokyo street

Tomohiro Kato - who originally claimed to be a member of the notorious yakuza crime syndicate but later retracted the statement - began the bloodbath after driving a two-ton truck into a crowd of shoppers in the Akihabara area and hitting three, terrified witnesses said.

The 25-year-old, who told police 'I came to kill' and 'I am tired of the world', then jumped out and began shouting at pedestrians before launching a frenzied stabbing spree.

Tomohiro Kato, wearing glasses, is detained by police officers

Probe: Police and ambulance officers investigate the stabbing scene in Tokyo's Akihabara shopping district

Six men, aged 19 to 74, and a 21-year-old woman were killed.

Within minutes of starting his attack police had arrested Kato, who was said to be 'grunting and roaring' as he slashed at his victims.

A fleet of ambulances attended the scene as the screams of pedestrians echoed around the district, which is popular with young Japanese people.

Rescue workers battled on the blood-soaked streets to save the 18 victims' lives, but at least seven have so far died, police have confirmed.

An ambulance worker pushes a victim on a stretcher at Tokyo's Akihabara shopping and amusement district

Tokyo TV news station NHK reported that Kato had told them he was 'tired of life'.

Akihabara, traditionally home to retailers of electronics and gadgets, has become synonymous in recent years with Japan's expansive "nerd" culture of video games, comic books and outlandish fashion.

Popular with locals and tourists, the area is often packed on weekends and would have been at its busiest during the attack.

Aftermath: A forensic officer inspects a patch of blood

One 19-year-old witness said: 'The man jumped on top of a man he had hit with his vehicle and stabbed him with a knife many times.

'Walking toward Akihabara Station, he slashed nearby people at random.'

Another said she saw a stabbing victim collapsed on the road, lying unconscious in a 'large pool' of blood.

Another, a man in his 40s, said: 'It is shocking. I came here often. This is unbelievable.'

And a middle-aged woman who also saw the carnage simply said: 'I am shaking.'

Toshiyuki Miyake, a spokesman for the Tokyo Fire Department, said five of the victims had gone into cardiac arrest.

Packed: The Akihabara district, known as Electric Town, is popular with Japan's computer game and comic book-obsessed youth

Once rare, stabbing attacks have become more frequent in Japan in recent years as violent crime has increased.

In one of the worst attacks, a man with a history of mental illness burst into an elementary school in Japan in 2001 and killed eight children. The killer was executed in 2004.