A 9-year-old boy died from heatstroke after being left alone in his mother's car for about 90 minutes on a sweltering day in the city of Nara, prefectural government officials said Tuesday.

The boy was found unconscious on Monday afternoon in the locked car in a parking lot in the city. He was rushed to a hospital but was pronounced dead in the early hours of Tuesday.

The boy's mother was quoted by the officials as saying that she went to a nearby hospital at around 1:30 p.m. after handing her car keys to her son and telling him to come later, while leaving the windows closed and engine shut off.

After returning to the parking lot, she found her son collapsed and immediately called an ambulance. The emergency crew had to break the car's window to free the boy.

The temperature in Nara reached 34.1 degrees Celsius at its peak on Monday, according to the Meteorological Agency.

Also on Tuesday, police in Shizuoka Prefecture arrested a 25-year-old man whose 1-year-old son died in a car after being left behind for about two hours while the man played pachinko on July 8.

Several similar deaths have been reported this summer, including the case of a mentally disabled 19-year-old man who died on July 13 after being left in a car for six hours at a welfare facility in Saitama Prefecture.