Photo/Illutration Shizuoka prefectural police enter the Kawasaki Kindergarten School in Makinohara, Shizuoka Prefecture, to search it on the morning of Sept. 6. (Akari Uozumi)

MAKINOHARA, Shizuoka Prefecture--Prefectural police searched Kawasaki Kindergarten School in Makinohara on the morning of Sept. 6 after a child was found unconscious with no vital signs in the school bus and later died.

Police believe that 3-year-old China Kawamoto was left in the bus for more than five hours after it arrived on the morning of Sept. 5 and that she may have suffered heatstroke.

Around 10 officers entered the premises of the kindergarten just after 9 a.m. on Sept. 6 to begin a search on suspicion of professional negligence resulting in death.

According to prefectural police, the school bus in question is a large van with capacity for 18 passengers.

The usual bus driver was on unexpected leave on Sept. 5, so Tatsuyoshi Masuda, a 73-year-old board chairman of the kindergarten, drove it that day to fill in.

When the bus was heading to the kindergarten that morning, there were eight people on board, including six students, Masuda, and a temporary staffer in her 70s.

Masuda and the temporary staffer told police they do not remember whether they made sure that young China had gotten off the bus, sources said. Police believe China was not ushered off the bus after it arrived at around 8:50 a.m. that morning.

China was found sometime around 2:10 p.m. that day when a staff member entered the bus, which had been left sitting in a parking lot outside the kindergarten, to move it before taking students back to their homes.

Police suspect China suffered heatstroke, as the temperature in Makinohara on Sept. 5 topped 30 degrees at its peak.

The Japan Meteorological Agency defines a day where the temperature reaches between 30 and 35 degrees as a "manatsubi” (full-summer day).

According to the Shizuoka prefectural government, the kindergarten had 158 students as of May 25, and it is staffed by 39 people, including part-time workers and assistants. It is a registered "kodomoen" center for child care and education.

The incident follows a similar tragedy in July last year in Nakama, Fukuoka Prefecture.

A 5-year-old boy died of heatstroke after he was left in a nursery school bus from the morning until the evening.

Following the boy’s death, the education ministry, the health ministry, and the Cabinet Office issued a joint notice to prefectures and municipalities in August last year on the safe operation of school buses.

The notice asked local authorities to encourage nursery schools, kindergarten schools and registered kodomoen centers in their areas to implement measures to ensure the safety of students on school buses.

It recommended assigning a staff member who can look after the students to be aboard the bus in addition to the driver.

It also recommended that staff keep track of the number of students as they get on and off the bus, ensure that no student is left on a bus when they exit the vehicle and share that information between them.