The State Electricity Regulatory Commission (SERC) has activated its highest possible emergency response and promised all-out efforts to restore power disrupted by a 7.8-magnitude earthquake that hit the southwestern Sichuan Province, the worst in more than three decades.

The quake, whose epicenter was in Wenchuan County, 159 km northwest of the Sichuan provincial capital of Chengdu, disrupted electricity supply in central and northwestern regions, the SERC said.

It's too soon to know how seriously the grid has been damaged, but the class-one emergency response, activated by SERC President Wang Xudong, sheds some light on its gravity. Class one is the top of five levels.

The SERC has ordered generation and transmission companies to determine as fast as possible the impact on the industry: workers hurt or killed and damage to facilities. It has also ordered all concerned to remain alert for hidden dangers.

The companies were also urged to take "practical and feasible measures" to prevent accidents that could result from quake aftershocks and other forms of earthquake-induced disasters.

Rescue workers who rushed to deal with the emergency should be cautious while working against the clock to restore power supplies, the SERC said.

Executives of power supply companies were required to be in "command on the spot" and "stay on top of the overall situation."

To secure power supply, the SERC also ordered hydropower plants to monitor dams in quake-hit areas and keep close touch with local governments and flood-control command agencies.

Officials at China Huadian Corporation, a centrally-administered power generator, said it had lost contact with its enterprise in the epicenter, although operations in other quake-ravaged regions had resumed.

Another major power generator, China Guodian Corporation, reported only temporary interruptions in operations in Sichuan. Seven workers injured by stones rolling from a construction site in Dagangshan were hospitalized.

The company said its hydropower plants in Gongzui and the Nanyahe River Valley in Sichuan were operating normally despite strong tremors on Monday afternoon.

State Grid said that the quake had cut the electrical load in Sichuan by 4 million kilowatts, paralyzing one 500-kv power station and five 220-kv power stations. Plants in western Sichuan including Jiangyou, Jintang, Baozhusi, Maoxian County and Dazhou Dongyuan were cut off from the grid.

In northwestern Shaanxi Province, the electrical load shrank by 1.5 million kilowatts on Monday, with two transformer sub-stations and three power generators malfunctioning, it said.

But the trunk power grid was operating smoothly, and the situation had improved overnight, with the lost electrical load recovering, State Grid said.

The emergency came just months after more than 6 million power staff were thrown into a 40-day fight to restore services to areas of China hit by an unusually severe round of winter weather. Storms cut electricity to 110 million people in 170 counties and damaged 36,740 transmission lines.