(Beijing, CHN) - Authorities in a southern Chinese province have ordered schools to take more care after two children died when they were left on hot school buses during the summer, Xinhua news agency said.

The hands of one victim, a five-year-old girl, were swollen when her body was discovered, indicating she must have been pounding at the windows of the bus to try to get help, the report said.

No one could see her because the windows of the bus were darkly tinted.

The body of the other victim, a three-year-old boy, was only discovered seven hours after he was left inside a separate bus. Both children were found to have suffocated, Xinhua reported on Tuesday.

Both incidents took place in the last week of August, one of the hottest months in southern China's Hainan province, with daytime temperatures in the low-30s Celcius (high-80s Fahrenheit).

The local education authority issued an emergency circular on September 1 demanding that schools take more care to ensure that all children leave the bus.

"The accident was due to poor awareness of individual school safety. The province must sound the alarm," the notice on the department website said.

Hainan now has about 1,000 illegal schools where safety standards are often overlooked, it quoted the provincial primary education director Wang Xian as saying.

Even before the deaths last week of the two young children, the provincial authorities had already shut 37 illegal schools for safety violations and ordered 66 others to improve or face closure, the report said.

The education department told AFP its spokesman was not available for comment.