File photo shows a worker's feet stained with oil following a crude spill in China's northeastern Liaoning province. An oil spill off China's eastern coast kept hidden from the public for weeks has caused long-term environmental damage that will hurt the area's fishing industry, state media reported Tuesday.

An oil spill off China's eastern coast kept hidden from the public for weeks has caused long-term environmental damage that will hurt the area's fishing industry, state media reported Tuesday.

Dead seaweed and rotting fish could be seen in waters around Nanhuangcheng Island in Shandong province, near the site of an oil spill that began "in early or mid-June", but was only made public on Friday, the China Daily said.

"The environmental impact caused by the oil leak is long-term," the newspaper quoted an local fisheries association official surnamed Xiao as saying.

Nanhuangcheng Island is about 75 kilometers (45 miles) from the offshore oil field in Bohai Bay where the leak happened.

"The oil leak will definitely influence the fishing industry nearby," Xiao said, adding the extent of the impact was still being assessed.

Meanwhile, state-owned China National Offshore Oil Corporation (CNOOC) tried to stem anger over its failure to warn the public about the spill, saying government authorities were aware of the incident all along.

"We reported the spills to authorities soon after they took place and treatment of the spills is under supervision," CNOOC spokesman Jiang Yongzhi was quoted as telling the Global Times.

The spill at one point had grown into an "oil belt" about three kilometres long and 30 metres wide -- larger than previously reported, the paper said.

The spill was first reported by a member of the public on the popular Chinese micro-blogging site Sina Weibo on June 21.

CNOOC confirmed nine days later that US oil company ConocoPhillips, which operates the Penglai 19-3 oil field where the leak originated, first reported oil on the surface of the sea "in early or mid-June", the China Daily said.

CNOOC said cleanup work was almost finished and the spill had been brought under control.

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(c) 2011 AFP