A 22-year-old Danish man has been arrested and charged with manslaughter.

The doctor was on a condolence visit to the suspect's home with a nurse and caregiver to pay respects to his deceased family member, NHK and other Japanese media say.

John T Earnest was identified as the author of a rambling, violently anti-Semitic, anti-Muslim manifesto found posted on the internet under his name minutes before the shooting began.