China and European Union nations have reaffirmed their commitment to a global plan to slow climate change after US President Donald Trump began undoing Obama-era plans for deep cuts in US greenhouse gas emissions.

Trump's order on Tuesday, in line with a campaign promise to bolster the US coal industry, strikes at the heart of the international Paris Agreement in 2015 to curb world temperatures that hit record highs in 2016 for the third year in a row.

Many nations reacted to Trump's plan with dismay and defiance, saying a vast investment shift from fossil fuels to clean energy such as wind and solar power is under way, with benefits ranging from less air pollution to more jobs.

Chinese foreign ministry spokesman Lu Kang, whose government cooperated closely with former US President Barack Obama's administration on climate change, said on Wednesday that all countries should "move with the times".

"Regardless of how other countries' climate policies change, China as a responsible developing country will not change its commitments, goals, policies and actions related to climate change," he said.

European Climate Commissioner Miguel Arias Canete said the EU saw the Paris agreement as a "growth engine" for creating jobs and new investment opportunities.

"Donald Trump's attempt to turn the US into a Jurassic Park run by dinosaur energy will eventually fail," said Hans Joachim Schellnhuber, Director of the Potsdam Institute for Climate Impact Research.

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Trump did not say whether he would pull out of the Paris Agreement, a pact agreed to by almost 200 nations that seeks a shift from fossil fuels this century as the cornerstone of efforts to limit heatwaves, floods, droughts and rising sea levels.

Trump's main target is Obama's Clean Power Plan, which required US states to slash carbon emissions from power plants, and was key to abiding by the US pledge under the Paris Agreement to cut emissions by 2025 to between 26 and 28 percent below 2005 levels.

'Serious step backwards'

The fear is that less action by the US, the number-two greenhouse gas emitter behind China, will cause other nations to roll back their own goals. The pact has been ratified so far by 141 nations ranging from Pacific Island states to OPEC oil producers.

The Paris Agreement lets each country set domestic targets for restricting greenhouse gases and foresees no sanctions for non-compliance. Trump has sometimes called global warming a hoax, but has also said he has an open mind about Paris.

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Still, Trump's rowback is likely to undercut a core principle of the Paris Agreement that all national plans, due to be submitted every five years this century, have to be ever stronger and reflect the "highest possible ambition".

A formal withdrawal from the Paris Agreement could trigger far wider criticisms, perhaps calls for import taxes on US goods.

Laurent Fabius, the former French foreign minister who was an architect of the Paris agreement, denounced Trump's moves as "a very serious step backwards".

German Environment Minister Barbara Hendricks warned Washington that it could lose out on energy deals going forwards.

"A shift into reverse [gear] now will only hurt themselves in terms of international competitiveness," she told Sueddeutsche Zeitung, a German daily newspaper.

Echoing that view, Danish Energy and Climate Minister Lars Lillehold said there had been "a significant momentum for the green transition" as green technologies have become cheaper.

In London, a spokesperson for the British Department for Business, Energy and Industrial Strategy reaffirmed Britain's commitment to tackling global climate change.

Speaking in Brussels, Izabella Teixeira, former Brazilian environment minister, said Trump's decision was a mistake.