China has rejected claims that it has moved ahead of the United States as the world's biggest energy consumer.

Zhou Xian, an official with China's National Energy Administration, said on Tuesday that an assessment by the International Energy Agency (IEA) was flawed.

"The IEA's data on China's energy use is unreliable," Xian said.

The Financial Timesand the Wall Street Journal cited a senior IEA official as saying the Asian giant had taken over the top spot in 2009, earlier than expected.

The Financial Times quoted Fatih Birol, the IEA chief economist, as saying: "In the year 2000, the US consumed twice as much energy as China; now, China consumes more than the US."

According to the IEA, China consumed 2.252 billion tons of oil equivalent of energy in 2009, from sources that included coal, nuclear power, natural gas and hydroelectric power - at least four per cent more than the US.

'Less energy-efficient'

The United States still uses far more energy than China on a per capita basis, but China is less energy-efficient, the report said.

The IEA, the energy strategy branch of the Paris-based Organisation for Economic Co-operation and Development, said the data was still preliminary but that the trend was clear.

China has embarked in recent years on an aggressive campaign to secure overseas energy supplies and satisfy sky-rocketing demand fuelled by its fast-expanding economy and citizens' increasing consumerism.

At the end of 2009, China announced ahead of the Copenhagen climate change summit that it would embark on a major energy efficiency drive to curb growth in its world-leading greenhouse gas emissions.

It has set a goal of generating 15 per cent of its energy from renewable sources, mainly wind and water by 2020.

The IEA's Birol told the Financial Times that while the United States had improved its energy efficiency by 2.5 per cent annually over the past decade, China had only notched up a 1.7 per cent annual improvement.

China still depends on coal for about 70 per cent of its energy needs. It has surpassed Japan as the world's largest coal importer, despite its own vast coal resources.