BEIJING - China will unveil its national plan to tackle global warming next month, including concrete measures to cut carbon dioxide emissions, a top climate change official said on Thursday.

Gao Guangsheng, head of the Office of the National Coordination Committee for Climate Change, said the plan, to be announced on April 24, would include policies for cutting back greenhouse gases but declined to comment on whether it would give an overall national target.

"We will make clear what policies and (in) what areas we plan to reduce greenhouse gas emissions," Gao told the Renewable Energy Finance Forum in Beijing.

China may become the world's top emitter of greenhouse gasses as early as this year, analyst estimates based on the country's latest energy data suggest.

Gao declined to comment on that forecast, or an International Energy Agency one that it will overtake the United States before 2010, because he said the country does not have an accurate idea of its own emissions.

An inventory is now under way but results could take up to three years to come through, he added.

But 35 developed nations that have agreed to cut emissions under the Kyoto Protocol want others to do more.

Gao also ruled out any possibility of an emissions trading exchange in the next two to three years, although he had been present at the launch of a UN scheme which officials had said would include carbon trading.

"No Chinese official said there would be an exchange," Gao told Reuters on the sidelines of the forum.

His office had earlier posted a notice denying reports of the exchange plans, but UN officials had said they were still working with Chinese counterparts on some kind of blueprint.