BEIJING - China's hydropower output dropped 24.5 percent year-on-year to 56.87 billion kilowatt-hours (kWh) in September as a result of decreased runoff from major rivers, according to the nation's top economic planner.

The September decrease was 9.9 percentage points higher than August's decrease, the National Development and Reform Commission (NDRC) said in a statement on its website.

As of the end of September, the adjustable water and hydropower reserves of the country's major hydropower plants stood at 104.9 billion cubic meters and 28.1 billion kWh, down 18.5 percent and 36 percent year-on-year, respectively, the NDRC said.

The dramatic drop in hydropower reserves will have a negative effect on electricity production and supply, the NDRC noted.