Meanwhile, a senior official who told reporters that the explosion didn't cause any pollution has reportedly been found dead.
Investigators will look into the causes of a Nov. 13 chemical plant explosion and the spill of 100 tons of benzene into the Songhua River, the official Xinhua News Agency said.
The country's chief industrial safety official warned that anyone who tried to hide the cause of the Nov. 13 chemical plant explosion that poisoned the Songhua River in the country's northeast will also be punished.
"Anyone, who were found guilty of dereliction of duty, will be harshly dealt with," said Li Yizhong, director of the State Administration of Work Safety, quoted by Xinhua.
"People who are found to have provided false information to investigators will also be punished severely," Li was quoted as saying. "Any move trying to cover up the cause of the accident and any passive attitude toward the probe are deemed deception and a defiance of law."
However, the report didn't say whether investigators would target the cause of the greatest public anger, accusations that Communist Party officials tried to cover up the spill, which disrupted water supplies to millions of people and strained ties with Russia.
Chinese media say local Communist Party leaders tried initially to conceal the spill of 100 tons of benzene and other toxic chemicals from environmental officials, the public and each other. An environmental official said earlier that the failure to report the slick immediately to Beijing cost China its best chance of minimizing the damage.
The government didn't announce that the Songhua had been poisoned with benzene until Nov. 23, the day that the major city of Harbin was forced to shut down running water to 3.8 million people.
Any investigation of party officials is usually carried out by the party's own discipline department, not civilian officials such as Li. The party typically must turn over an offender to prosecutors before civilian authorities can pursue a criminal case.
A deputy mayor of Jilin who told reporters the chemical plant explosion had not led to any pollution was found dead at home Tuesday, a pro-Beijing Hong Kong newspaper reported Wednesday.
Ta Kung Pao said the cause of death for 43-year-old Wang Wei was still unclear.
Wang worked on containing the aftermath of the explosion, running a team responsible for evacuating residents, according to the report.
Also Wednesday, another town on the Songhua was warning residents to stock up on water and stop using the river, according to state media.
The town of Fujin, with about 115,000 people, relies on groundwater wells, local party newspaper Jiamusi Daily said. The report didn't say whether running water would be suspended, but that families were told to store water for daily use.
The disaster prompted Beijing to apologize both to the Chinese public and to Russia, a key diplomatic partner.
Li, the safety official, is in charge of a Cabinet-level team assigned to investigate the chemical plant explosion and will report directly to senior Chinese leaders, Xinhua said.
The director of China's environmental protection agency has resigned and the general manager of the chemical company blamed for the spill was removed from his post.
But the environmental regulator also has a seat on the party's 198-member Central Committee, the heart of Chinese power, and there has been no indication that he might lose that post.
Premier Wen Jiabao visited Harbin three days later and promised to investigate the disaster, though he didn't say whether authorities would take action on the failure to inform the public promptly — the biggest complaint by environmentalists and ordinary Chinese.
In Jiamusi, where the slick arrived Tuesday, the government is conducting tests for benzene every hour on water drawn from wells, the city's main water source, the city administration's secretary, Zhang Danhong, told reporters.
Jiamusi shut down some wells used by its main water plant on Friday because they were deemed to be too close to the river and authorities worried about contamination.
A new water plant that draws groundwater from wells farther from the river was rushed into operation ahead of schedule on Monday, and Zhang said it should be sufficient to meet the city's needs until the slick passes.
About half of the residents in 279 households on Liushu Island, a river island in Jiamusi, were temporarily evacuated, Xinhua said. Those remaining behind had stored up enough potable water for one month, it said.
The city of 480,000 people has so far budgeted 8.1 million yuan for measures meant to deal with the contamination, Zhang said.
The figure adds to the mounting economic toll from the disaster.
Upstream, Harbin's city government is borrowing 640 million yuan to cope with the spill's aftermath, according to state media.