A group of Chinese fishermen is suing ConocoPhillips for damages allegedly caused by a huge oil spill at an offshore field operated by the US energy giant, their lawyer said Friday.

The early-June spill leaked more than 3,000 barrels of oil and oil-based mud -- a substance used as a lubricant in drilling -- off China's eastern coast, drawing widespread public criticism and warnings from Chinese authorities.

The group has filed a civil lawsuit in a court in the eastern city of Qingdao asking the Houston-based firm to pay 30 million yuan ($4.7 million) to more than 200 fishermen living there, Yi Jiafeng told AFP.

"In environmental pollution lawsuits, we follow the principle of 'inverse responsibility of providing proof' -- the victims detail the damage and the respondent must provide counter evidence," he said.

ConocoPhillips was not immediately available for comment.

Environmental groups and local fishermen have accused the US firm and its Chinese state-run partner CNOOC of initially covering up the spill, which was discovered in June but only made public nearly a month later.

But both firms deny the allegations. ConocoPhillips says it cooperated with authorities as soon as the accident occurred in Bohai Bay in northeast China.

"Any release of oil, no matter the size, is too great," it said in a statement on its website.

CNOOC, meanwhile, said last month all the leaks had now been identified and sealed, the official Xinhua news agency reported.

The fishermen involved in the lawsuit claim they lost a total of 164,000 yuan invested in clam seedlings and 17,000 undersea cages -- only 3,000 of which had clams left alive after the spill, the official Beijing News reported.

The State Oceanic Administration -- the government agency that supervises and manages China's seas -- has also said it will sue ConocoPhillips over the leak.

But an earlier civil lawsuit connected to the spill was dismissed by a court in the northern port of Tianjin for lack of evidence, the Beijing News said.

Yi, who filed the lawsuit Friday, said it would take seven days for the Qingdao court to decide whether or not it would accept the case.