SHANGHAI (AFP) - China has fined 10 Japanese auto parts firms more than US$200 million (S$250 million) for price-fixing, authorities said Wednesday, in what state media called the biggest-ever penalty for violating the anti-monopoly law.

The companies were found to have implemented monopoly pricing agreements for more than 10 years, the National Development and Reform Commission (NDRC) regulator said in a statement.

It fined them a total of 1.24 billion yuan (S$250 million), in what state broadcaster CCTV said was the biggest fine China had imposed since its anti-monopoly law took effect in 2008.

"The companies... unlawfully affected prices of auto parts, finished vehicles and bearings in China and harmed the interests of downstream manufacturers and consumers," the NDRC statement said.

Sumitomo Electric was fined the most - 290.4 million yuan - of the seven car parts firms penalised for fixing auto parts prices between January 2000 and February 2010, according to the statement, the others being Denso, Aisan, Mitsubishi Electric, Mitsuba, Yazaki, Furukawa Electric.

NSK, JTEKT, and NTN were fined for price collusion over bearings between 2000 and June 2011, the NDRC added, with NSK ordered to pay 174.9 million yuan.

Two other companies, Hitachi Auto Parts and Nachi, which makes roller bearings, were found culpable but exempted from the penalties for taking the initiative to inform authorities and providing critical evidence on the monopoly agreements, according to the NDRC.

The companies all pledged to rectify their sales policies and comply with Chinese law, it said.

The NDRC, one of several Chinese government bodies that investigates monopoly actions, said in early August that it was probing auto firms including Audi, Chrysler as well as the 12 Japanese companies for possible violations.

It is the latest in a series of inquiries in various fields which have raised investor concerns that foreign firms are being targeted.

State media have reported that more than 1,000 companies in the country's auto sector, both domestic and foreign, are currently involved in anti-monopoly probes by the government.