A father in western Japan was arrested Wednesday for allegedly inflicting injuries on his five-month-old son in 2021 that left the child with severe and likely permanent brain damage.

Yudai Arata, 26, is accused of causing his second-born son to suffer severe head trauma by unknown means at the family's home in Izumiotsu, Osaka Prefecture, on Dec 4, 2021.

The now 1-year-old child sustained injuries including subdural bleeding and has been unconscious since the incident, Osaka prefectural police said. His prospects for recovery are slim, police believe.

The child was possibly shaken violently, resulting in the condition known as shaken baby syndrome, with police also saying they will investigate whether the abuse happened on multiple occasions.

Arata called emergency services on the night of the incident saying that his son was vomiting milk and had become pale. The baby was taken to hospital in a state of cardiac arrest.

He told police that the child's injuries were caused when he accidentally hit the boy's head while placing him on the floor to attempt heart resuscitation.

Arata, who has refused to comment on the allegations, has already been indicted for abuses and injuries inflicted on his eldest son when the child was eight months old.

He has been charged with biting the child on the elbow and throwing him onto a bed sometime between December 2019 and February 2020. Video footage of Arata assaulting his eldest son was found on his smartphone.

In a separate case, a 25-year-old mother was arrested Wednesday in Yokohama near Tokyo for allegedly severely burning her three-year-old daughter in 2019 by pouring boiling water on her back.

The woman, named Kaho Hashimoto, has denied the accusation.

At the time of the incident, she explained she had mistakenly directed hot shower water at her daughter. But police arrested Hashimoto after consulting physicians and determining that the act, which occurred sometime between Feb. 28 and March 1, 2019, was intentional.