The incident came to light late on Monday when a passer-by noticed blood flowing out of the closed shutter of Toru Sasaki's shop of used industrial machines attached to the family's house in Tokyo.

Sasaki, 52, is believed to have killed his wife, Kazuko, 49, and his mother Tokuko, 85, according to Jiji Press news agency and other Japanese media.

The younger of the Sasakis' two sons, 15, was found with his hands almost cut off. He told a rescue official, 'Dad did this,' before falling into a coma at a hospital, the reports said.

News reports said the two women had head injuries, while the father's wound was in the neck. A blood-stained hatchet with a 20-centimetre blade was found at the scene.

A note believed to have been written by the man was also found, which included phrases such as, 'I only intended to take mother,' and 'I couldn't protect my people,' Jiji Press said.

The bodies were identified by the elder son, 18, who had been away for college entrance exams.

Gruesome details of the case shocked the nation at the end of a holiday weekend, with television vans rushing to the area where small factories and houses are clustered together.

Neighbours told networks that the family seemed to be on good terms with one another but may have been under pressure financially.

A police spokesman said four people had been found collapsed but declined to disclose further details. -- AFP