China National Petroleum Corp. said Thursday a vital pipeline has resumed operations after an explosion caused the country's largest reported oil spill.

Cleanup efforts — marred by the drowning death of a worker, his body coated in crude — continued over 165 square mile (430 square kilometer) stretch of water blanketed in thick, dark oil Thursday, after an official warned the spill posed a severe threat to sea life and water quality. The slick emptied beaches as its size doubled Wednesday.

It remained unclear exactly how much oil has escaped the pipeline six days after it exploded for reasons unknown at a busy northeastern port. State media has said no more oil is leaking into the Yellow Sea.

China Central Television earlier reported an estimate of 1,500 tons of oil has spilled. That would amount roughly to 400,000 gallons (1,500,000 liters) — as compared with 94 million to 184 million gallons in the BP oil spill off the U.S. coast.

CNPC, which owns the pipeline at the port of Dalian, said more than 400 tons of oil had been cleaned up by 9 a.m. Wednesday, according to a report posted on its website Thursday.

The company, Asia's biggest oil-and-gas producer by volume, also said the pipeline was repaired and resumed operations Monday, now pumping 45,000 tons of crude oil a day. The blast had reduced oil shipments from part of China's strategic oil reserves to the rest of the country.

Greenpeace China released photos Wednesday of inky beaches and of straw mats about 2 square meters (21 square feet) in size scattered on the sea, meant to absorb the oil.

Fishing in the waters around Dalian has been banned through the end of August, the state-run Xinhua News Agency reported.

"The oil spill will pose a severe threat to marine animals, and water quality, and the sea birds," Huang Yong, deputy bureau chief for the city's Maritime Safety Administration, told Dragon TV.

Officials, oil company workers and volunteers were turning out by the hundreds to clean blackened beaches, but questions were raised about the effectiveness of the efforts.

"We don't have proper oil cleanup materials, so our workers are wearing rubber gloves and using chopsticks," an official with the Jinshitan Golden Beach Administration Committee told the Beijing Youth Daily newspaper, in apparent exasperation.

"This kind of inefficiency means the oil will keep coming to shore ... This stretch of oil is really difficult to clean up in the short term."

But 40 oil-skimming boats and about 800 fishing boats were also deployed to clean up the spill, and Xinhua said more than 9 miles (15 kilometers) of oil barriers had been set up to keep the slick from spreading.

The cause of the explosion that started the spill was still not clear. Friday's images of 100-foot-high (30-meter-high) flames at China's second largest port for crude oil imports drew the immediate attention of President Hu Jintao and other top leaders.