China acknowledged on Tuesday that it is the world's biggest greenhouse gas emitter, as it called on the United States to ensure climate change talks opening next week make progress.

Speaking at a briefing ahead of the UN talks in Mexico, Xie Zhenhua, China's top climate change official, told reporters: "Our emissions volume now stands at number one in the world.

His comments appeared to be the nation's first public recognition of the fact.

Up to now, Chinese officials had not clearly acknowledged the nation's world-leading emissions, which had nevertheless been confirmed by scientists and international organisations such as the International Energy Agency.

They preferred to emphasise the need to use emissions per capita -- where China is far behind developed countries -- as a benchmark.

The November 29 to December 10 talks in the Mexican resort of Cancun are set to open with deep rifts between developed and developing nations, mainly China and the United States -- the two biggest sources of carbon emissions.

The United States wants China to commit to emissions cuts but Beijing argues that it and other developing nations should be exempt from such curbs as they need to grow their economies and lift people from poverty.

It also notes that the emissions of industrialised, mainly Western, countries over the centuries are historically responsible for the build-up of carbon in the atmosphere.

"We hope the United States will play a leadership role and drive the entire process of negotiations," said Xie, vice director of the National Development and Reform Commission -- China's top economic planning agency.

He announced no new Chinese proposals for the talks but vowed the nation would seek to limit growth in its emissions.

"We will not allow our emissions to increase unchecked. China is taking decisive actions to slow down our emissions so that our emissions peak can come at an early date," he said, without giving a timetable.

He also reaffirmed Beijing's position that developed nations must bear the brunt of efforts to curb emissions of the greenhouse gases blamed for global warming and climate change.

"We will absolutely not accept any obligations that go beyond developing countries' abilities," he said.

"Developed countries have historical responsibilities and must assume their obligations. This is something we must adhere to," he said, when asked whether China should take on more of a role at the Cancun summit.

China has set a 2020 target of reducing carbon emissions per unit of gross domestic product by 40-45 percent from 2005 levels. That amounts essentially to a vow of energy efficiency, but its emissions will continue to soar.

It has refused to estimate when its carbon emissions will peak and then begin to fall, although officials have indicated it could take decades.

The talks in Cancun are the latest round of negotiations in a long-running UN effort to forge a global treaty to limit carbon emissions, which are blamed for trapping heat in the Earth's atmosphere.

Xie said the ultimate goal of climate change negotiations should be "a result that not everyone is satisfied with but that everyone can accept."

Scientists say rising temperatures could lead to an increase in catastrophic extreme weather.