China has been under-reporting its coal consumption for years, experts said Wednesday after official statistics were revised upwards by hundreds of millions of tonnes a year.

Pollution is a growing concern in the world's second-largest economy, whose cities are regularly blanketed by choking smog -- much of it the result of burning coal, which provides most of China's primary energy.

The updated figures suggest that Chinese emissions of greenhouse gas carbon dioxide -- already the world's largest -- are bigger than previously thought.

The news comes weeks before a UN summit in Paris, where nations will seek an agreement on tackling climate change, in the face of divisions over how the burden should be divided between countries.

The 2014 version of China's official statistics yearbook says the country consumed 3.53 billion tons of coal in 2012.

But in the latest edition, the same number for the same year was given as 4.12 billion tons -- a rise of nearly 600 million tons, or almost 17 percent.

The increase was equivalent to over 70 percent of the United States' annual coal consumption, said the New York Times, which first reported the changes.

The figures implied that China's annual carbon dioxide emissions had been underestimated by more than Germany's total yearly output, the newspaper added.

Figures as far back as 2000 were changed, according to comparisons by AFP of different editions of the China Statistical Yearbook, published by the National Bureau of Statistics (NBS).

The NBS did not immediately explain the reasons for the revisions to AFP.

There are widespread doubts over the accuracy of official statistics in China, which critics say can be subject to political manipulation.

But at a coal forum in Beijing, Zhou Fengqi, an adviser to the National Development and Reform Commission, China's top planning body, said: "The new figures are more accurate than before."

The data has depended on incomplete provincial statistics, he said.

"Now the national figures have progressed and more accurately reflect the situation."

Song Guojun, professor of environmental economics at Renmin University, said the adjusted figures were "certainly more reliable".

"Coal is a very common thing in China. At the county level and below, and even at the city level, there were many sources of coal use which did not make it into the official statistics-gathering mechanism," he said.

- Duty to humanity -

The US Energy Information Administration said in September that Chinese coal consumption on an energy content basis from 2000 to 2013 was 14 percent higher than previously estimated.

Coal production was up to seven percent higher in the same period, it added, citing preliminary Chinese data.

A shift towards more environmentally friendly development is China's "duty and contribution to humanity" as one of the world's largest countries, Premier Li Keqiang said this week during a visit by French President Francois Hollande.

China has pledged that its carbon dioxide emissions will peak by "around 2030".

Yang Fuqiang, senior climate change advisor at the Natural Resources Defense Council, a US environmental campaign group, said the new coal statistics would not necessarily affect the Paris negotiations since Beijing's commitment was "only about a peak rather than the total volume of CO2 emissions".

He added that the increased figures did not rule out widely-expected possibility that China's coal use could peak before 2020, as economic growth slows and shifts away from reliance on heavy industry.

But he added that "there will be more concern about the volume of emissions" from China.