China's September power output continued growing by double-digits for an eighth consecutive month even as the world's second-largest economy reported a slowdown in economic activity.

Reports from the National Bureau of Statistics on Tuesday showed China's electricity generation grew 11.5 per cent to 386.1 billion kilowatt-hours in September from a year ago. The latest figures pulled generation growth in the first nine months down to 12.7 per cent from 13 per cent in the first eight months, and 13.5 per cent in the first half of the year.

At 12.87 billion kWh per day, the September output was lower than the previous three months. A few months ago, output hit above 13 billion kWh owing to the summer heat that drove monthly generation to surge.

The decline is consistent with China's economic expansion, which has slipped in recent quarters in the middle of tightening policies and softening demand for exports.

A number of local governments fast-tracked cutting energy consumption in the last months of the year to meet year-end energy efficiency goals, eventually pushing power generation to single digits in the final four months.

Output from thermal power plants grew 19.5 per cent year on year to 314.6 billion kWh last month and generation from nuclear stations reached 15.1 per cent to 7.69 billion kWh.

Electricity from hydropower plants fell 20.2 per cent to 56.85 billion kWh from a year earlier.