More than 100 chemical plants beside China's rivers pose safety threats, the country's environment chief has warned.
A chemical plant blast in November caused a serious spill
Zhou Shengxian said the plants were surveyed after a chemical spill in November poisoned the water supply for millions of people in the north-east.
The affected river, the Songhua, has since frozen over, but Mr Zhou said its water would be safe once it thawed.
He said the plants identified as unsafe were being investigated, and the findings would be published.
This was likely to happen some time after the Lunar New Year holiday which begins at the end of the month, he said.
He acknowledged that in the past the government had valued economic growth above environmental degradation, but that its priorities were now changing.
"The Chinese government has made a very timely and determined decision to stop the conventional approach of development, which could be characterised as 'pollution and destruction first, treatment later'," he told a news conference.
He said that a total of 21,000 chemical factories had been found to be located along China's rivers and coastline.
"Since the locations are quite a big problem, we need to take measures to avoid any future consequences of possible accidents," he said.
More than half the plants were found to be located along two of China's most important rivers, the Yangtze and Yellow rivers, which are relied upon by millions of people.
The state environment agency said the chemicals in the Songhua had since dissipated and that the amount that sank into the river bed was "limited".
"As a result, the chemical content in the river will not rise above the state standards for water quality when the river thaws in spring," the administration was quoted as saying by the official Xinhua News Agency.
Consequently, fish from the river were safe to eat, the agency said.
One hundred tonnes of the carcinogens benzene and nitrobenzene were dumped into the Songhua after an explosion on 13 November at a PetroChina chemical factory in the north-eastern province of Jilin.
The chemicals moved hundreds of kilometres downstream, forcing water supplies to be cut in the town of Harbin, leaving some of its 3.8m people without water for five days.
Mr Zhou's predecessor as head of the State Environment Protection Administration, Xie Zhenhua, resigned soon after the leak, and criticism of the government's response.