BEIJING – China and environmental observers said cleanup efforts on the country’s largest reported oil spill were progressing Thursday, but the environmental and economic damage was clear.

The cleanup — marred by the drowning of a worker this week, his body coated in crude — continued over a 165-square-mile stretch of the Yellow Sea off the northeastern city of Dalian, one of China’s major ports and strategic oil reserve sites.

China National Petroleum Corp. said Thursday that the pipeline that exploded and caused the oil spill last Friday had resumed operations. The blast had reduced oil shipments from part of China’s strategic oil reserves to the rest of the country. The cause of the explosion was still not clear.

The company, Asia’s biggest oil and gas producer by volume, also said more than 400 tons of oil had been cleaned up by 9 a.m. Wednesday, according to a posting on its website.

The environmental group Greenpeace China released photos Thursday of local fishermen cleaning up oily sludge at Weitang Bay with shovels, and of an employee scooping up dead snails at Guotai Water Products Farm, about a half mile from the site of the explosion and spill.

“Dalian’s seafood farming and tourism industries have taken critical hits,” Greenpeace China said in a statement.

The group estimated 10,000 shellfish farms have been contaminated.