The US is guilty of "obstructing" the global fight against emissions, China said Wednesday, as Beijing seized the climate agenda by vowing to go carbon neutral by 2060 -- a target welcomed by environmentalists despite its patchy detail.

The goals, which include a pledge to reach peak emissions in 2030, are the most concrete yet announced by China, which is the world's biggest polluter and accounts for a quarter of the planet's greenhouse gas blamed for rising temperatures.

They also open a new divergence in relations with the US, which are already pinched by squabbles over trade, tech, defence and human rights.

Speaking to the UN General Assembly, Chinese President Xi Jinping on Tuesday renewed his support for the Paris climate accord and called for a green focus as the world recovers from the Covid-19 crisis.

Under President Donald Trump, the United States -- the world's second-largest polluter --  pulled out of the agreement, blaming China for the stalled momentum on tackling global emissions. 

"This clearly... seriously obstructs the progress of reducing global emissions," China's foreign ministry spokesman Wang Wenbin said in a statement on Wednesday.

"What qualifications does such a country have to criticise China," he asked, citing America's hunger for plastics and its export of waste. 

In his speech to the UN, Xi set China out as a climate leader, saying the Paris accord "outlines the minimum steps to be taken to protect the Earth," and that "all countries must take decisive steps to honour this agreement".

China aims to have "C02 emissions peak before 2030 and achieve carbon neutrality before 2060", Xi said.

'Nuanced picture' 

In addition to its embrace of global emissions-busting deals, China already feeds nearly 15 percent of its energy demands with non-fossil fuels, spokesman Wang added.

China's "installation of renewable energy stands at 30 percent of the world total", he said.

But experts say the picture is more nuanced, with massive investments continuing at home and overseas in coal and other fossil fuels.

China currently has 135 gigawatts of coal-power capacity either permitted or under construction, according to Global Energy Monitor, a San Francisco-based environmental group. 

That equates to about half the total coal-power capacity in the US.

The Paris climate deal commits nations to limit global temperature rises to near pre-industrial levels through a rapid and sweeping drawdown of greenhouse gas emissions. 

Less ambitious objective 

Welcoming China's pledge, EU commission president Ursula von der Leyen Tweeted "a lot of work remains to be done".

The 2060 objective is still a decade later than the date set by dozens of small states as well as European powers. 

But it was roundly applauded by experts as a significant step to inject momentum into the flatlining Paris accords.

Joeri Rogelj, a climate expert at Imperial College London's Grantham Institute, called Xi's pledge "unexpected and eye-opening".

"All in all, China's announcement is a defining moment that resets the ambition of global climate action," he said.

If China reaches carbon neutrality by 2060, it could lower projected global warming by 0.2 to 0.3 degrees Celsius, the biggest potential dip tracked since the Paris Agreement was drafted in 2015, Berlin-based non-profit Climate Action Tracker said in a statement Wednesday.

But notes of caution remain in a fast-growing country weaned on fossil fuels.

The "devil will be in the details" said Helen Mountford, vice president for climate and economics at the World Resources Institute in Washington.

Others questioned whether China would follow its own guidelines as it pursues a global infrastructure-building binge -- for example, if it will still back coal plants in Africa.

Trump on attack 

Xi's tone at the UN contrasted sharply with that of Trump, who called the Paris accord -- negotiated by his predecessor Barack Obama -- unfair to the United States.

Trump says he is standing up for US constituencies such as coal miners and has loosened environmental rules, although individual US states such as California have insisted on fighting climate change on their own.

"Those who attack America's exceptional environmental record while ignoring China's rampant pollution are not interested in the environment," Trump said in a UN speech shortly before Xi spoke.

The future of the Paris accord will be partly determined on November 3 as Trump runs for re-election against Joe Biden, who has pledged to return the United States to the agreement and move toward carbon neutrality by 2050