Chinese Premier Li Keqiang has ordered an investigation into the case of four "left behind" children who apparently committed suicide by drinking pesticide in a poor part of southwestern China, as millions of workers leave loved ones to find work.
In many rural parts of China, children are left in villages to be looked after by grandparents or other relatives while their parents work in the booming cities.
They are either not able to join their parents because of their jobs, or because in many cases they lack the paperwork needed to live in urban areas and access services like schools and health services.
The four children, one boy and three girls aged from five to 13, were left alone at home in Bijie in Guizhou province and died after drinking pesticide on Tuesday, state media said.
Once Li found out what had happened he was "extremely concerned", the central government said in a statement on Friday.
Li ordered the relevant government departments "increase supervision" so that social security mechanisms do not "become a mere formality".
Those found to have not done their job properly will be "held accountable", the statement added.
State television said that the eldest boy, Zhang Qigang, left a letter saying "this has been planned for a long time, and today it is the time to go".
The Bijie government said that it had begun an investigation and that several officials had already been punished. Yang Qian, the Communist Party secretary of Tiankan Township in Bijie City, and Chen Mingfu, the township head, had both been sacked and criminal charges may be brought, it added.
State media said that the father of the four children worked outside of the province, while the mother was also not around. They had to live on 700 yuan ($112) a month their father sent them, had dropped out of school and lived off corn their father had planted last year.
In 2012, five homeless children in the same city died of carbon monoxide poisoning after lighting a fire while seeking shelter in a rubbish bin.
China aims for 60 percent of the population of almost 1.4 billion to be living in cities by 2020, turning millions of rural dwellers into consumers who could be a driving force for the world's second-largest economy.
Chinese leaders have pledged to loosen their grip on residence registration, or hukou, to try to remove obstacles to the urbanization drive. Such registrations prevent migrant workers and their families from getting access to education and social welfare outside their home villages.
