TOKYO (AFP) - A 32-year-old Japanese man was arrested on Friday (Oct 6) on suspicion of stabbing his daughter to death and has admitted deliberately torching the house in which his wife and four other children were found dead, police said.

The man, Hirobumi Komatsu, told the authorities he started the fire at the family's home in Hitachi City, some 100km north of Tokyo, deputy police chief Mitsuru Kaneko told Agence France-Presse.

Police discovered five bodies at their apartment after the blaze was extinguished in the early hours of Friday, he said.

One little girl was found in critical condition with stab wounds and later died in hospital.

The children - a girl and four boys - were aged between three and 11, while the sixth victim was their mother, police said, citing what the suspect told them.

"We first learnt about the incident when the man showed up at the police station to report it," the deputy police chief said.

The father could also be facing arson charges, police said.

The deaths of the five other victims are under investigation, Mr Masataka Suzuki, another senior police official, told AFP.

"We are investigating to see if the cause of death of the five others was the fire or something else," he added.