TOKYO, JAPAN - THE 25-year-old factory worker arrested at the scene of a frenzied attack on a crowd of shoppers in Tokyo that left seven dead has told police he wanted someone to stop him, domestic media said on Thursday.

Tomohiro Kato posted dozens of warning messages on a mobile phone website ahead of the attack, media have said, raising questions about whether the crimes could have been prevented.

In one message posted on Sunday, Kato said he was going to kill people in Akihabara, a popular area for buying discount electronic goods.

He is suspected of having driven a truck into a crowd of shoppers in Akihabara later that day, killing four, then got out and stabbed three more to death, injuring a further 10 in a crime that horrified Japan.

Newspapers published details of Kato's advance planning, saying he had visited the area the day before the attack and questioned several people about road closures.

'I wanted someone to call the authorities and stop me,' the regional Tokyo newspaper quoted Kato as telling police. He also said he felt sorry for the seven who died, the paper said.

Black-clad family members and friends gathered to mourn the victims at funerals and wakes on Wednesday and Thursday.

Friends of Mai Muto, a 21-year-old music student, wiped tears from their eyes as they walked into a hall near their university in Tokyo, some carrying their musical instruments to play a last farewell.

'She was a kid with a great future,' the Nikkei newspaper quoted Muto's former elementary school teacher as saying. 'I wish I could give her my own life.'