BEIJING, Oct. 16 -- China's electricity consumption, a key barometer of economic activity, continued stable expansion in September, official data showed on Monday.

Power usage climbed 9.9 percent from a year ago to 781.1 billion kilowatt-hours last month, according to the National Energy Administration.

Power consumption by primary industries increased by 8.6 percent year on year, while power consumption by secondary and tertiary sectors gained 8.7 percent and 16.9 percent, respectively.

Residential power usage saw a year-on-year increase of 6.6 percent to 103.5 billion kilowatt-hours in September, the administration said.

In the first three quarters, the country's electricity consumption rose 5.6 percent from a year earlier to 6.86 trillion kilowatt-hours.