May 12 (Bloomberg) -- China's strongest earthquake in 58 years damaged power plants and transmission lines, forcing companies to idle some generators in Sichuan and Shaanxi.

About 5.5 gigawatts, nearly 1 percent of the nation's generation capacity, was idled in the two provinces after today's quake, according to a report by the official Xinhua News Agency, citing data from the State Grid Corp. of China. Sichuan, the epicenter of the quake, lost 4 gigawatts of capacity.

Six substations were damaged in Sichuan, disconnecting power plants in the province's western regions from the national grid, while in neighboring Shaanxi two substations and three generating units were hit by the temblor, Xinhua reported.

Some 900 students were feared buried by a mudslide caused by the quake, which struck 90 kilometers west-northwest of Chengdu, the capital of Sichuan. PetroChina Co. and China Petroleum & Chemical Corp., the country's biggest oil companies, said they were yet to assess damage to refineries and natural gas fields in the province.

Sichuan holds about 40 percent of China's natural gas reserves and produced about 22 percent of the nation's output in 2006, according to China National Petroleum Corp., PetroChina's parent, and BP Plc's annual energy report.

Resources Companies

The extent of damage to China's resources companies was still unclear because disruptions in telephone networks cut off local staff from their head offices in Beijing, Shanghai and Guangzhou. The quake took out more than 2,000 China Mobile Ltd. base stations, Vice President Sha Yuejia said in a broadcast on state-run China Central Television.

China National Coal Group., the country's third-biggest producer of the fuel, hasn't received any reports of damage to its mines, spokesman Jiang Chun said by phone from Beijing.

Local staff at Sichuan Power Corp., a unit of State Grid Corp., haven't contacted the company's headquarters in Beijing, Director Peng Xiashu said by telephone. ``We have lost contact and we aren't sure if there is any damage,'' Peng said.

At least one major power installation said it wasn't hit by the quake. China Three Gorges Project Corp., the nation's biggest hydropower operator, said the hydropower plant and the transmission lines connecting the dam to the outside grid were unaffected by the temblor.

Three Gorges

``Operations at the project are normal,'' Jin Changjiang, the dam operator's spokesman, said by mobile phone from the central province of Hunan.

Today's quake, the biggest in China since a magnitude 8.6 tremor struck Tibet in 1950, caused buildings to shake in Beijing more than 1,500 kilometers away. It was the world's strongest since September when a 7.9-magnitude temblor hit Indonesia, according to the USGS Web site.

To contact the reporters on this story: Wang Ying in Beijing at wang30@bloomberg.net;

Last Updated: May 12, 2008 08:49 EDT