Berlin (AFP) - China and Europe took the lead Thursday on forging on with the Paris climate accord, as fears grew US President Donald Trump would pull Washington out of the landmark deal.

President Donald Trump waits for the arrival of Vietnamese Prime Minister Nguyen Xuan Phuc to the White House in Washington, Wednesday, May 31, 2017. AP Photo/Susan Walsh Berlin (AFP) - China and Europe took the lead Thursday on forging on with the Paris climate accord, as fears grew US President Donald Trump would pull Washington out of the landmark deal.

After a day of rumours about the Republican leader's plans, with some aides reportedly saying a withdrawal was likely and others saying no decision had been taken, Trump said he was ready to make his stance known.

"I will be announcing my decision on Paris Accord, Thursday at 3:00 P.M. The White House Rose Garden. MAKE AMERICA GREAT AGAIN!" the US leader said in a tweet, punctuating the post with his campaign slogan.

Hours ahead of his 1900 GMT announcement, the world's biggest carbon emitter China pledged to stay the course on implementing the 2015 accord.

Premier Li Keqiang said it was in China's own interest to do so, and urged other countries to do likewise.

"China will continue to implement promises made in the Paris Agreement, to move towards the 2030 goal step by step steadfastly," Li said in a Berlin joint press conference with German Chancellor Angela Merkel.

"But of course, we also hope to do this in cooperation with others," added Li, as Merkel hailed China's pledge.

China has been investing billions in clean energy infrastructure, as its leaders battle to clear up the notorious choking pollution enveloping its biggest cities, including Beijing.

Li, who was due to travel to Brussels for a summit with the European Union later Thursday, was expected to stress the same message there.

China and the US are responsible for some 40 percent of the world's emissions and experts have warned that it is vital for both to remain in the Paris agreement if it is to have any chance of succeeding.

The leader of Asia's other behemoth, Indian Prime Minister Narendra Modi, had said Tuesday, also in Berlin, that failing to act on climate change would be "morally criminal".

Trump raised alarm bells when he refused to sign up to a pledge on the deal at last week's G7 meeting in Italy.

Merkel on Saturday labelled the result of the "six against one" discussion "very difficult, not to say very unsatisfactory".

German Chancellor Angela Merkel, right, and China's Premier, Li Keqiang, left, look at each other during a joint press conference as part of a meeting at the chancellery in Berlin, Germany, Thursday, June 1, 2017. AP Photo/Michael Sohn

'That's not acceptable'

With media reports swirling that Trump had decided to pull Washington out of the accord, America's international allies and Trump's domestic opponents have lashed out at the billionaire.

The White House did not confirm those reports, and it was unclear whether Trump would fully scrap US participation, merely water down US emissions objectives -- or surprise everyone with a decision to follow the status quo.

A US withdrawal would come less than 18 months after the historic 196-nation pact was adopted in the French capital, the fruit of a hard-fought agreement between Beijing and Washington under Barack Obama's leadership.

European Commission President Jean-Claude Juncker hit out at Trump's purported decision.

"I am a transatlanticist. But if the US president in the next hours and days says that he will get out of the Paris accord, then it's the responsibility of Europe to say: that's not acceptable.

"It's not about the future of the European people, it's above all about the future of people elsewhere," warned Juncker on Wednesday.

He noted that it would take three or four years to exit from the Paris deal, and revealed that world leaders had sought to explain that to Trump at the G7 summit.

"As it appears, that attempt failed," said Juncker. "But a rule is a rule. And everyone must respect it. Not everything that is a rule, and not everything that stands in an international agreement is fake news."

European Union President Donald Tusk also issued a plea to Trump on Twitter, saying: "please don't change the (political) climate for the worse."

President Donald Trump welcomes Chinese President Xi Jinping at Mar-a-Lago state in Palm Beach, Florida. Reuters/Carlos Barria

'I'll get back to you'

The Paris agreement commits signatories to efforts to reduce greenhouse gas emissions that cause global warming, which is blamed for melting ice caps and glaciers, rising sea levels and more violent weather events.

They vowed steps to keep the worldwide rise in temperatures "well below" two degrees Celsius (3.6 degrees Fahrenheit) from pre-industrial times and to "pursue efforts" to hold the increase under 1.5 degrees Celsius.

Since taking office on January 20, Trump, who has called climate change a "hoax", has sent contradictory signals on the Paris deal.

When asked on Tuesday whether Trump believes human activity is contributing to climate change, White House spokesman Sean Spicer told reporters, "Honestly, I haven't asked him that. I can get back to you."

Trump's new head of the Environmental Protection Agency, climate sceptic Scott Pruitt, has said he wants Washington to quit the Paris deal.

But other top Trump advisers, including his daughter Ivanka and Gary Cohn, the head of the president's National Economic Council, are said to favour staying in the treaty.

A dozen large companies including oil major BP, agrochemical giant DuPont, Google, Intel and Microsoft, have also urged Trump to remain part of the deal.