China's State Oceanic Administration?launched a site inspection on Thursday to check?the claim?of U.S. oil giant ConocoPhillips?that it has sealed off an oil spill that polluted north China's Bohai Bay.

Oil coats pooled water, sand and rocks on the shore at Changdao, a major fish farming island in Shandong province. A leak on an offshore oil platform was discovered in northern Bohai Bay on June 4; this photo was taken on July 8.?[China Daily]

ConocoPhillips China, owner of two oil spill platforms which polluted 5500 square kilometres of water in China's northern Bohai Bay, said it had already sealed off the leaks ahead of an Aug. 31 deadline.

The company said it had submitted a report to the SOA, showing that the company has met the SOA's requirements to seal off the sources of the spill and eliminate the risk for further leaks.

Lin Fangzhong, an official with the inspection team sent to the site, said they were using satellites, aircraft, sea vessels and even underwater robots to conduct a thorough examination of the company's plugging measures.

"We are using robots which can acquire underwater images to verify the seal as well as aircraft and sea vessels to take water samples on the surface," Lin said.

Even if the examination's results show no oil on the surface, it would not prove that pollution is on the decline as already-leaked pollution will have a more negative impact on marine sediments and oceanic ecosystems, according to Zhou Qing, deputy chief engineer of the SOA's northern monitoring center.

"The Iraq War brought oil pollution to waters in the Persian Gulf that has lasted for more than 20 years," Zhou said. "The center will continue to monitor the ecosystem in Bohai Bay."

SOA confirmed late Wednesday that it has received the report but said the administration still needs to conduct site inspection and expert evaluation to verify the company's conclusions, according to Xinhua.

On Thursday morning, strong winds and 5- to 6-meter waves at the spill site at the Penglai 19-3 oil field forced clean-up boats as well as the vessels of China's maritime authorities supervising the clean-up work to return to port.