Finance ministers from the world's biggest economies were battling on Saturday to halt a bid by US President Donald Trump's administration to roll back hard-fought pledges on trade and climate.

Representatives from G20 nations have gathered in the picturesque western German spa town of Baden Baden since on Friday for a meeting clouded by concerns over Trump's "America First" policy and scepticism towards climate change.

Trump, whose tough protectionist talk helped win him the presidency, has withdrawn the US from a trans-Pacific free trade pact and attacked export giants China and Germany.

On Thursday, he also revealed a budget plan that would make good on a campaign pledge to drastically scale back environment-related funding.

That stance has grated Washington's partners, who are trying to persuade US Treasury Secretary Steven Mnuchin to renew a long-standing G20 anti-protectionism commitment and uphold an international deal on climate won only after years of painful negotiations.

But talks have so far failed to produce a breakthrough for consensus, and the clock is ticking down to the close of the two-day session when a final statement is due to be published.

A source close to the negotiations said that "there will be nothing on climate in the communique — a sign of the discord".

"The US says that on this issue, the position hasn't been clearly defined in Washington and they need time," added the source.

On trade, Washington is calling into question the current international trade regulation system under the World Trade Organisation — a move which the source said is "unacceptable".

French Finance Minister Michel Sapin said leaders would be asked to step in when they meet in Hamburg if no agreement can be found.

"Our heads of states are meeting in a few weeks. On subjects that are so important, it's not up to the finance ministers to block or to walk back on the issue, there will not be any backsliding on such fundamental issues," he said.

Carried to power on the back of a political storm over deindustrialisation in vast areas of the US, Trump vowed in his inauguration speech to "follow two simple rules: buy American and hire American." 

Trump himself insisted at a tense Washington press conference Friday following his first meeting with German Chancellor Angela Merkel that "I'm a free trader but also a fair trader".

He also rejected a description of his policies as "isolationist." 

But the differences between the two were laid bare as Merkel took the opportunity to push back against Trump's calls for individual trade deals with European countries, suggesting instead that the White House "come back to the table and talk" about a stalled US-European Union pact.