Huaneng Power International Co Ltd, China's top power producer, said it posted a net loss of 470.33 million yuan ($68.85 million) in the first half to June, against a net profit of 2.96 billion yuan a year earlier, mainly due to the surging coal prices.

In a statement filed with Shanghai Stock Exchange, the company said the loss was equal to 0.04 yuan per share, against a profit of 0.25 yuan per share last year.

It said that rising coal costs pushed up unit fuel costs at its mainland power plants by 34.03 percent year-on-year to 226.78 yuan per kWh.

The company's revenue was up 30.83 percent at 30.79 billion yuan in the first half, driven by higher power output, it said.

Huaneng Power produced 91.45 billion kWh of electricity in the first six months, a rise of 13.43 percent from a year earlier.

China has raised power prices twice in recent months and slapped temporary controls on coal prices. Huaneng Power said these moves have improved the company's operations to some extent.

Last week, China raised the on-grid power price paid to producers of coal-fired electricity by up to 0.025 yuan per kilowatt-hour.

Following the move, the company raised its on-grid power tariff by an average 22.51 yuan per megawatt hour (MWh), or 5.67 percent.

The company indicated the tariff hike is still not sufficient to offset its operating losses.

"For the third quarter, the company's losses are expected to increase if coal prices remain at high levels and no further power price hike is made by the government," it said.

The company added that it will take measures to ensure sufficient coal supplies and seek government support to improve its operations.