The five boys aged about 10 died of carbon monoxide poisoning after apparently burning charcoal inside the trash container to keep warm, Xinhua news agency said.

A trash collector discovered the bodies on Friday morning in the dumpster in the city of Bijie in Guizhou province, according to the Beijing News.

Autopsies showed carbon monoxide poisoning was the cause of death, Xinhua quoted sources in a local branch of the ruling communist party as saying.

It said leftover burnt charcoal was found inside the dumpster, indicating that the boys might have been burning charcoal for heat before they died.

Calls to Bijie police and city officials went unanswered Sunday.

The Friday night low temperature in the mountainous city was 6 degrees Celsius (43 degrees Fahrenheit).

Photos uploaded onto the Internet showed that the dumpster is about 1.5 metres (about five feet) long and 1.3 meters wide, and has an airtight lid, Xinhua reported.

The tragedy has sparked an outcry on the net, it said.

A post on Sina Weibo, a Twitter-like microblogging service, had more than 2.5 million hits as of Sunday evening.

While some users accused the local government of negligence, others said the parents of the children were also to blame, according to the news agency.

"It reminded me of The Little Match Girl by Hans Christian Andersen. Isn't it that such things only happen in fairy tales?" wrote one user called Saludika.

"What a cold world this must be for the five children!" said another, Lu_Yao.