A man stabbed all four members of a family he was dining with at a restaurant near Tokyo on Sunday evening, killing a 6-year-old girl, police said.

The police arrested Motomu Oda, 46, at the "izakaya" pub in the city of Chiba on suspicion of attempted murder. The father of the girl has told investigators the suspect was a brother of his wife.

Oda spoke incoherently shortly after he was arrested but later admitted to the stabbings, the police said, adding they will carefully examine whether he is mentally competent and can be held criminally responsible.

The girl was taken to hospital unconscious and later pronounced dead. Her 44-year-old father was injured in the thigh and her 42-year-old mother in the upper half of her body but neither was in a life-threatening condition. The fourth family member, the girl's 1-year-old sister, suffered a minor injury.

Oda, a former Chiba city assembly member, started shouting before stabbing the four with a knife around 7 p.m. on Sunday, the police quoted the father as saying. He added that they were dining together after the suspect traveled from Okinawa Prefecture.

The police are investigating whether the attack was premeditated as Oda is believed to have brought a knife with him when he went to the restaurant located near JR Inage Station.