A mayor apologized to residents of two Chinese villages where more than 600 children were sickened by lead poisoning, saying a nearby smelter targeted by angry protests would not reopen until it meets health standards, state media said Tuesday.

Authorities have promised to relocate hundreds of families within two years, the official Xinhua News Agency said, but residents were not reassured.

"If they relocate us to these nearby places, who can guarantee that our babies will be safe?" said farmer Deng Xiaoyan, a resident of Sunjianantou, one of the affected villages. She said a recent test showed her 3-year-old daughter had high levels of lead.

Environmental problems have escalated as China's economy booms, sometimes prompting violent protests. Counting on lax enforcement of regulations, some companies find it easier and cheaper to dump poisons into rivers and the ground rather than dispose of them safely.

At least 615 of 731 children in two villages near the Dongling Lead and Zinc Smelting Co. plant in Shaanxi province's Changqing town have tested positive for lead poisoning. Some had lead levels 10 times the level China considers safe.

Lead poisoning can damage the nervous and reproductive systems and cause high blood pressure, anemia and memory loss. It is especially harmful to young children, pregnant women and fetuses, and that damage is usually irreversible, according to the World Health Organization.

The mayor of Baoji city, which oversees Changqing, arrived at the plant Monday as hundreds of villagers were protesting, tearing down fences and blocking traffic outside the factory, Xinhua reported. Dai Zhengshe apologized and said the plant will not be allowed to open again until it meets health standards, the report said.

Villagers had been enraged by the plant's defiance of the Aug. 6 order to suspend operations, Xinhua said. Fighting between angry parents and scores of police broke out Sunday, and trucks delivering coal to the plant were stoned.

The mayor said the plant halted production only on Monday because of safety reasons. "We had to make sure the gas in the pipeline was exhausted before the plant was finally shut down," Dai said in the Xinhua report.

A man surnamed Ma who lives in Madaokou — the other of the badly affected villages, about 500 yards (meters) from the factory — said residents believed at least two villagers were taken from their homes by police Monday night. He said the Baoji city government sent officials to his village Tuesday to try to pacify residents.

"They wanted to persuade us not to cause trouble, but they didn't provide any solution to our problems," Ma said by telephone.

Associated Press journalists saw no sign of workers at the factory Tuesday, while about 50 police officers guarded the compound. Another 50 sat in police buses. The windows of the factory's reception area and security office were shattered.

A few hundred children were being tested Tuesday for lead poisoning in a third village, Luobosi.

Dr. Pascal Haefliger, a health and environment expert with the World Health Organization in Geneva, said lead stays in the body for years after exposure and continues to affect brain development and the nervous system in growing children.

"Medical treatment exists, but will not be successful in removing all the lead from the body," he said.

Xinhua said authorities have promised to relocate hundreds of families within two years, with the building of new homes about 3 miles (5 kilometers) from the plant starting last week.

Deng, the farmer, cradled her daughter and said she thought those houses would still be too close.

"There is lead in the air, the air is polluted, everything is polluted," she said.