MENGXI VILLAGE, China — On a chilly evening early last month, a mob of more than 200 people gathered in this tiny eastern China village at the entrance to the Zhejiang Haijiu Battery Factory, a maker of lead-acid batteries for motorcycles and electric bikes. They shouldered through an outer brick wall, swept into the factory office and, in an outpouring of pure fury, smashed the cabinets, desks and computers inside.

News had spread that workers and villagers had been poisoned by lead emissions from the factory, which had operated for six years despite flagrant environmental violations. But the truth was even worse: 233 adults and 99 children were ultimately found to have concentrations of lead in their blood, up to seven times the level deemed safe by the Chinese government.

One of them was 3-year-old Han Tiantian, who lived just across the road from the plant. Her father, Han Zongyuan, a factory worker, said he learned in March that she had absorbed enough lead to irreversibly diminish her intellectual capacity and harm her nervous system.

“At the moment I heard the doctor say that, my heart was shattered,” Han said in an interview last week. “We wanted this child to have everything. That’s why we worked this hard. That’s why we poisoned ourselves at this factory. Now it turns out the child is poisoned too. I have no words to describe how I feel.”

Such scenes of heartbreak and anger have been repeated across China in recent months with the discovery of case after case of mass lead poisoning — together with instances in which local governments tried to cover them up.

In the past 2 1/2 years, thousands of workers, villagers and children in at least nine of mainland China’s 31 province-level regions have been found to be suffering from toxic levels of lead exposure, mostly caused by pollution from battery factories and metal smelters. The cases underscore a pattern of government neglect seen in industry after industry as China strives for headlong growth with only embryonic safeguards.

Chasing the political dividends of economic development, local officials regularly overlook environmental contamination, worker safety and dangers to public health until forced to confront them by episodes like the Haijiu factory riot.

A report by Human Rights Watch released Wednesday states that some local officials have reacted to mass poisonings by arbitrarily limiting lead testing, withholding and possibly manipulating test results, denying proper treatment to children and adults and trying to silence parents and activists.

“What we are trying to underscore is how little has been done to address the massive impact of lead pollution in China,” Joe Amon, the organization’s health and human rights director, said in an interview. “It really has affected a whole generation of kids.”

In more developed nations, where lead pollution has been tightly regulated for decades, a pattern of lead poisoning like China’s would most likely be deemed a public-health emergency.

High levels can damage the brain, kidney, liver, nerves and stomach and, in extreme cases, cause death. Children are particularly susceptible because they absorb lead more easily than adults.

“No blood lead level has been found to be safe for a child,” Dr. Mary Jean Brown, chief of the lead poisoning prevention branch of the Centers for Disease Control and Prevention, said in an interview last week.

Chinese leaders have acknowledged that lead contamination is a grave issue and have raised the priority of reducing heavy-metal pollution in the government’s latest five-year plan, presented in March. But despite efforts to step up enforcement, including suspending production last month at a number of battery factories, the government’s response remains faltering.