An explosion at a Jilin chemical plant on 13 November poured 100 tonnes of cancer-causing benzene compounds into the Songhua River, but the State Environmental Protection Administration said that for the following four days it received no reports from provincial authorities.
That meant the "best opportunity" to control the spill had been lost, the state-run newspaper reported Administration Vice-Minister Wang Yuqing as telling a national teleconference.
"A reckless pursuit of economic growth and a lack of emergency response mechanisms have seen China experiencing a high rate of environmental disasters," Wang was quoted as saying.
The toxic slick forced officials in Harbin, a city of 9 million people, to shut off water.
The slick has since passed through the city and is making its way downstream through the northeast province of Heilongjiang towards the Russian border.
Spill moves on
On Friday, the slick was passing through the Heilongjiang town of Dalianhe, where water supplies were cut off on Thursday.
"A reckless pursuit of economic growth and a lack of emergency response mechanisms have seen China experiencing a high rate of environmental disasters"
State Environmental Protection Administration
The town of 67,000 was relying on well water and tapping into supplies from neighbouring communities, a town official said by telephone. He added that the length of the cut-off depended on how long it would take for the pollution to pass through.
Downstream in Jiamusi, the city has launched a back-up scheme to tap groundwater sources in a project that will start operation before the belt of pollution reaches, likely by next Tuesday, the official Xinhua news agency reported.
The local government was also having deeper wells dug across the city, the report said.
The initial attempts to cover up the spill were a blow to President Hu Jintao's drive to boost government accountability and Wang said there could be yet more environmental disasters that local officials keep quiet.
By the end of November, 36 major pollution accidents had been reported, Wang said without giving details, adding there could be many more that have gone unreported.
Regional governments were also giving tacit consent to the discharge of pollutants into rivers and some had approved polluting businesses that the central government had banned,
"Local environmental protection bureaus need to increase their ability and improve their equipment to supervise and handle pollution," he said.
Less than half of China's provinces have emergency plans in the event of environmental accidents, Wang added.