BEIJING, China (CNN) -- China's largest oil company has apologized for an explosion that led to a toxic slick of benzene entering the Songhua River and the suspension of water services to the northeastern city of Harbin.An official with the China National Petroleum Corporation on Thursday apologized to the residents of northeast Heilongjiang province for the spill after a November 13 blast at a chemical plant owned by CNPC's Jilin Petrochemical company.Benzene, used in gasoline, is a cancer-causing substance. It can cause anemia, other blood disorders and kidney and liver damage.Water service in the city of Harbin had to be shut off after the spill of around 100 tons, which spanned 80 kilometers (50 miles) wide.The plant blast, which authorities blamed on human error at a tower that processed benzene, killed five people and forced the evacuation of tens of thousands of others.The contaminated water reached Harbin's water supply inlet at about 5 a.m. Thursday local time (2100 Wednesday GMT), and entered river sections across the city's urban areas, according to the state-run Xinhua news agency.Zeng Yukang, deputy general manager of the government-owned petrochemical plant CNPC, "expressed his sincere sympathy and deep apologies" to residents for the pollution, Xinhua reported.The vice-governor of neighboring Jilin province, where the plant is located, also offered his apologies, the news agency said.'Waited too long'Critics say the Chinese government waited too long to inform the people of Harbin and officials in Russia, where the pollution is expected to arrive in about two weeks.The government, which blamed CNPC for the disaster, didn't publicly confirm the river was polluted until 10 days after the accident.Besides the potential for an environmental disaster, the incident has turned into a public relations disaster for China, which until the past two days had not given residents timely information about the approaching spill.In an effort to appease the public, government officials, in a rare turnaround, began offering hourly updates.The polluted water from likely will reach the Heilongjiang River, called the Amur River in Russia, on the Sino-Russian border in around 14 days judging from the current flow speed, Xinhua reported."China is very concerned about the possible hazards to Russia and has informed its neighbor several times of the pollution," Foreign Ministry spokesman Liu Jianchao said at a news conference."Both have pledged to cooperate closely to handle the pollution."Earlier Moscow issued a statement to its neighbors asking them to communicate about matters potentially affecting Russia in a "timely manner."Jarred nervesChina defended its handling of the spill even as reports emerged of another explosion at a plant in southwestern region of Chongqing.More than 6,000 residents were evacuated after the blast, which killed one person and injured three, raising fears of benzene contamination, Reuters quoted the Southern Metropolis Daily as reporting.And in a sign of how the first accident has jarred national nerves about widespread pollution, Premier Wen Jiabao issued instructions demanding safe drinking water be ensured.Some of the 100 tons of pollutants from the first incident has already been absorbed because the density of the pollutants had dropped markedly, according to Zhang Lijun, deputy director China's State Environmental Protection Administration.The possibility of criminal charges in connection with the incident remained Thursday.Chinese environmentalists have said the country keeps experiencing such incidents because of poor risk management and poor corporate responsibility.Stronger legislation and more forceful implementation is needed to enforce safety standards, they say, amid the country's sizzling economic growthHarbin has cut off its water supply for at least four days, and has trucked in 700 tons of bottled water. New wells are being drilled to make up for the shortage.Schools in Harbin, the capital of Heilongjiang province, have closed and hospitals were put on standby to deal with any medical emergencies, although none were immediately reported.Officials have estimated the toxins may pass Harbin in about 40 hours, but residents -- who scrambled to save water in pails and bathtubs as well as cramming grocery stores to stock up on bottled water -- remained worried about long-term health effects, and many were taking no chances.Others worried about how the threat could affect Harbin's tourism industry. People flock each year to the city's Ice Festival to see sculptures carved out of ice.CNN's Jaime FlorCruz contributed to this report.