CHANGSHA - Police have detained four kindergarten employees following the death of a student who was left unsupervised on a school bus in south China's Hunan Province, local authorities said Friday.

The kindergarten head, bus driver, bus monitor and the child's teacher were all taken into police custody after the four-year-old child died on Thursday while under the care of a private kindergarten in Sixingang Township, Linli County, according to a spokesperson for the Communist Party of China county committee.

The boy got on the bus around 7 a.m., and was found unresponsive at 3 p.m. Thursday, when his relative came to collect him from school.

The cause of death is being investigated, but the spokesperson said as temperatures reached 32 degrees Celsius on Thursday, fatal heat stroke had not been ruled out.