A group of Chinese fishermen have sued ConocoPhillips in a US court, seeking over $130 million in compensation for an oil spill off China's coast last year, a lawyer advising them said Wednesday.

Thirty fishermen from the eastern province of Shandong this week filed the lawsuit against ConocoPhillips in the US city of Houston, Texas, where the oil giant is headquartered, Beijing-based lawyer Guo Chenxi told AFP.

Another 470 are also preparing to lodge suits, said Guo, one of the advisers to the fishermen.

The spill in June last year at the offshore Penglai field, jointly developed by ConocoPhillips and state-owned China National Offshore Oil Corporation (CNOOC), allowed more than 3,000 barrels of oil and oil-based mud -- used as a lubricant in drilling -- to vent into the sea.

ConocoPhillips said Wednesday it had not received any official notice of the lawsuits but that it was inappropriate for any such claims to be handled by US courts.

"(The suits) are not appropriate for US courts and should be dismissed," the company said in a statement sent to AFP.

Guo said the exact amount of compensation had yet to be set, but the 500 fishermen have initially claimed they suffered 870 million yuan ($137 million) in direct economic losses.

"The compensation they will demand will be much higher than that because it will take into account losses in the next decades and a punitive fine according to US laws," she said.

In the United States, the fishermen have retained lawyers from three firms including the Houston-based Bilek Law Firm, she said.

"We are confident... because the US lawyers specialise in oil-related pollution. They are very experienced," Guo said.

The two oil firms previously said they would pay a total 1.0 billion yuan in compensation for the spill. The funds were paid to the Ministry of Agriculture in March.

But Guo said that compensation package did not cover the fishermen in Shandong.

Environmental groups and local fishermen have accused ConocoPhillips and CNOOC of initially covering up the spill, saying it was discovered in June 2011 but only made public nearly a month later.

Both firms deny those allegations. ConocoPhillips says it cooperated with authorities as soon as the accident occurred.