Tens of thousands along the Beijiang river were without potable water after a state-owned smelting works last week released excessive amounts of the chemical, which can cause neurological disorders and cancer.

The major spill in Guangdong province's Shaoguan city was China's second in as many months after a benzene slick from a factory in northeast China cut tapwater to millions of city-dwellers for four days last month.

The two spills have focused attention on water pollution in a country where millions still lack safe drinking water and most rivers are polluted by industrial and human waste.

Officials this week had lowered a dam gate and released water from reservoirs upstream in Beijiang to try to slow the flow of the slick and dilute it as it headed towards the metropolis Guangzhou.

The government was now dumping a neutralizing chemical into the river, state media on Friday quoted officials as saying.

"Experts have been sent to release 'medicine' into the water to reduce its toxicity," the China News Service (CNS) quoted the director of the local China Environmental Supervision Station as saying.

"Currently there's a turn for the better in the water quality," said the official surnamed Li.

Tens of thousands of residents living upstream in Yingde city's outlying rural areas, however, told AFP that officials had cut their tap water altogether on Thursday.

Officials had finished a pipeline that brought water from a local reservoir, but it only serves the urban areas of Yingde.

In Longtoushan village, 7,000 cement plant employees and their families, and 3,000 nearby residents, were all relying on water supplied by fire engines, said Zhang Yongcai, the village chief.

The village has up to 200 wells, all of them in use, he said, but they could not provide sufficient water for the community.

"We have to go to public shower houses located in Wangfu town where people queue up for hours to take a shower," he said.

Guangdong's governor, Huang Huahua, was quoted Friday as warning residents not to use the polluted river water for agricultural use.

"We must ensure the information is told to every household and inform them not to use Beijiang water for irrigation and raising animals," Huang was quoted by CNS saying.

Guangdong's countryside is used for livestock and vegetable farming, and much of the produce are exported to neighboring Hong Kong and Macau, raising fears of economic losses after the spill.

In Zhang's village, the rice crop had already been harvested, but villagers' livelihood, were still affected, Zhang said. "The fishermen in our village can no longer make money from fishing in Beijiang," he said.

"It will take two months for us to get back to our normal life," Zhang said, adding that those responsible for the pollution "should be punished."

More than a week after the spill, the government had not yet announced whether anyone had been punished.

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