China has passed the United States to become the world's biggest energy user, according to the International Energy Agency. However, Chinese officials say that the IEA's data are unreliable.

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China was bound to overtake the US in terms of total energy consumption sooner or later, and according to IEA calculations, it happened in 2009.

One long-term factor behind this development is China's population – more than four times that of the US – with a growing appetite for consumer goods that need energy to use and to manufacture.

The other key reason is China's rapid economic growth, an annual average of 10% over the last two decades, compared with a much slower 2.6% in the United States. Much of China's economic growth has been in industry and construction, which are big energy users.

The timing of China overtaking the US also reflects the global financial crisis, which hit the American economy much harder and so had a bigger impact on the country's energy use.

China's new lead in energy consumption is yet another indicator of its growing influence in the global economy especially in international energy markets.

But while China's total energy consumption has, according to the IEA, overtaken the US, it's still far behind in terms of energy use per person, by a factor of more than three. Chinese officials have said the IEA's data are unreliable, and fail to account for what they call their relentless efforts to cut energy use and emissions.

The response probably reflects China's sensitivity to criticism of its growing global influence. But the IEA's analysis is not a criticism. A senior official at the agency described China's growing energy consumption as legitimate, considering its population.

Andrew Walker, BBC News, London