BEIJING (AFP) - The killing of four children by their poverty-stricken mother - who then committed suicide, followed by her husband - sparked online outrage and debate in China Tuesday over the gap between rich and poor.

Yang Gailan, 28, used an axe to kill her three daughters, aged six, five and three, and her five-year-old son, police in the northwestern province of Gansu said.

She committed suicide by drinking pesticide, they added in a statement online, and her husband Li Keying poisoned himself two weeks later, after the funerals.

The family had been among the poorest in Agushan village, reports said, but were denied a government low-income allowance by the village committee, which claimed their annual per person income put them above the poverty line benchmark of 2,300 yuan (S$470) a year.

Multiple media reports alleged corruption was a factor, saying their benefits had been cancelled because they had not bribed local officials.

"Ours is a brutal, man-eating society," said one poster on China's Twitter-like Weibo Tuesday.

The situation "exactly reflects the painful reality of the extent of China's poverty", wrote Xiang Songzuo, chief economist for the Agricultural Bank of China, on his verified social media account.

"On the one hand are the corrupt officials embezzling hundreds of millions at every turn and the rich spending thousands every day, fighting to compare who can spend more, while on the other side are those in such poverty they lose the hope of living."

Yang, Li and their four children lived with Yang's grandmother and father in a small, dirt-floored adobe house with three cows and 12 chickens, their most valuable possessions, the China Youth Daily reported.

Yang was still alive and able to speak when her grandmother found her lying in the grass by an empty bottle of pesticide, traces of blood, and the bodies of her children, it said.

"Why didn't you at least leave me Yifan?" her grandmother cried, referring to the eldest girl, her favourite, with whom she shared a bed every night.

Yang was taken to a local hospital and though she did not refuse treatment, she kept repeating "don't save me", according to the China Youth Daily.

China relaxed its strict one-child policy earlier this year to allow families to have two offspring, but even during the decades it was in effect, rural households were allowed two children if their first was a girl.

In many instances, those living in remote rural areas like Agushan without the resources to strictly enforce the law were able to have more.

China's boom has seen it rise to become the world's second-largest economy, but inequality remains stark and the Global Times newspaper, citing the National Bureau of Statistics, said 70 million people currently live below the poverty line, primarily in rural areas.

It quoted Dang Guoying, a rural development expert at the Chinese Academy of Social Sciences, saying: "This case shocked urban Chinese people living in developed eastern cities, because most of us cannot imagine that millions of Chinese people still live in poverty."