A series of pictures and videos of two Chinese boys, who were found hiding in the undercarriage of a bus, has sparked an online outcry about the plight "left behind" children in rural China.

The two boys, aged eight or nine, reportedly travelled about 80km to find their parents who work in the neighbouring province of Guangdong.

According to the Southern Morning Post newspaper, the boys who are from a poor village in southern Guangxi, were reported missing on 23 November by their school teacher.

They were later found on the same day in the undercarriage of a vehicle at a bus station.

The photos show the boys curled up in the bottom of the carriage, with their faces and body covered in mud, BBC reports.

Staff members at the bus station said they were surprised to find the children unharmed, given that the bus had had covered three miles along "steep slopes".

"These children's bodies were really thin, so the undercarriage was a good hiding space," one staff told the paper.

A staff member who helped the boys get down from the carriage said, "We finally came to understand that these two boys had been missing their mum and dad.

"They had hidden under the vehicle because they wanted, in vain, to find their parents."

China's Left-behind children

The "heartbreaking" pictures have shocked China's online community.

One user of the popular Chinese microblogging site Weibo said, "There are way too many young children in China now who are separated from their parents from a young age. Who is caring for them, and finding a solution to their problems?"

While another person pointed out that it was a "tragedy in society". A user also said that people need to pay more "attention to left-behind children".

As many as a third of children living in rural China come under what is known as "left-behind children"– a term used for "children under the age of 16 whose parents are migrant workers, or who have one migrant-worker parent with the other incapable of guardianship".

On the Road to School, a Chinese Non-governmental organisation, which works with these underprivileged children, stated that about 60% of the children living in rural settings see their parents less than twice a year.

While it is impossible to know the exact number of children who have been left behind in the Chinese countryside, it is obvious that it is a serious issue, the Shanghaiist website had earlier reported.