China, the world's top CO2 polluter, promised Tuesday to peak emissions within about 15 years, in a move widely hailed as a boost for the global effort to curb planet warming.

Beijing's eagerly-anticipated contribution to a roster of carbon-curbing pledges was announced by Prime Minister Li Keqiang when he met French President Francois Hollande in Paris.

The venue and timing were symbolic -- exactly five months to the start of a UN conference in the French capital that will be tasked with producing the first-ever climate pact binding all the world's nations.

China's official pledge, one of only a handful by developing nations so far, joins those of the United States and European Union with whom it jointly accounts for about half of the world's annual greenhouse gas output.

"China's carbon dioxide emissions will peak by around 2030 and China will work hard to achieve the target at an even earlier date," said a government announcement.

It also committed to cutting CO2 emissions per unit of GDP by 60-65 percent over 2005 levels by 2030, boosting the share of non-fossil fuel in primary energy consumption from 11.2 percent in 2014 to 20 percent, and increasing the volume of forest stock by about 4.5 billion cubic metres.

Hollande hailed the pledge as confirmation of China's commitment to an "eco-friendly society", and French Foreign Minister Laurent Fabius said it was "an excellent sign" for the November 30-December 11 Paris conference.

Green groups and think tanks said China's pledge, which formalises an undertaking made at a US-China summit last November, set an important political example.

"China now joins the United States, Europe and others with a credible, ambitious commitment to tackle climate change," said Bob Perciasepe, president of the Center for Climate and Energy Solutions, a US-based think tank.

"This is a clear sign that we're moving past the old developed-developing country divide to a new understanding that all major economies have to contribute their fair share to the global effort."

Added climate diplomacy expert Liz Gallagher of campaign group E3G: "This submission is critical to building momentum towards a climate deal in Paris."

China became the 16th of 195 parties to the UN Framework Convention on Climate Change (UNFCCC) to formally submit its pledge or "intended nationally determined contribution" (INDC). The 16 include the 28-member EU bloc.

These INDCs will be a crucial support for the highly-anticipated Paris agreement, which must take effect from 2020 with the goal to limit average global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels.

In its pledge, China underlines the importance of "common but differentiated responsibilities" -- an issue that divides rich and poor nations in the fractious UN climate process.

Developing nations insist the West has a bigger responsibility to slash emissions given its longer history of carbon pollution.

And they want assurances of finance and technology transfers to help poor and threatened nations make the switch to greener energy and adapt to unavoidable climate change.

Climate analyst Samantha Smith of green group WWF said it was commendable that China has made commitments "beyond its responsibility as a developing country."

But, along with the other pledges received, it was not ambitious enough to set the world on track for meeting the 2C target.

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"We hope that China will continue to find ways to reduce its emissions, which will in turn drive global markets for renewable energy and energy efficiency," said Smith.

Added Gallagher: "There is still time for China to ramp up ambition. These offers are the floor, not the ceiling of a deal in Paris."

Li Shuo, a climate analyst with Greenpeace China, said a dramatic decline in Chinese coal consumption, a big switch to green energy and the imperative to reduce air pollution, meant "the country can go well beyond what it has proposed today."

A recent study by two research institutes at the London School of Economics said China's greenhouse gas emissions, mainly CO2, may already peak in 2025, five years ahead of its target, on current trends.

According to the UN's Intergovernmental Panel on Climate Change (IPCC), a 2 C pathway requires annual greenhouse gas cuts of 40-70 percent by 2050, compared to levels in 2010 -- and to zero or below by 2100.

Current global emissions are about 50 gigatonnes CO2 equivalent, about a quarter by China alone.