Asia-Pacific ministers struggled Thursday to agree on a joint statement on free trade in a rare wrangle over a usually routine document as US negotiators dug in over protectionism, insiders said Thursday.

Global leaders from the Pacific Rim region are gathering in the Vietnamese city of Danang this week for the annual Asia Pacific Economic Cooperation (APEC) forum.

Russia's Vladimir Putin, US President Donald Trump, and China's Xi Jinping are among the power players who will attend the 21-member summit -- the latter pair giving speeches likely to present divergent visions on the future of global trade on Friday.

Ahead of their arrival, trade and foreign ministers are meeting to issue a joint statement detailing their common goals, normally something of a formality.

But this year they have been deadlocked, unable to reach a consensus before the arrival of global leaders.

Three diplomatic sources with knowledge of the talks said the cause was US negotiators sticking to 'America First' lines and pushing for more protectionist wording.

Trump has railed against free trade deals, describing them as bad for US jobs, and instead favouring a rebalanced "fair" trade system.

A press conference to discuss the statement was cancelled late Wednesday and negotiators worked into the small hours of Thursday morning in tense discussions trying to find a breakthrough.

"We are now feeling the Trump effect at APEC," one source with knowledge of the talks, told AFP.

"The US has concerns about references to free trade and protectionism," added a second source, requesting anonymity.

"It's the same as G20," a third source added, referencing the global gathering in March when leaders of the global economic forum for the first time dropped a routine pledge to keep world trade free and open, under US pressure.

Australian trade minister Steven Ciobo played down reports of discord.

"We're obviously having ongoing discussions about the statement, each country wants it to reflect their values," he told AFP.

"I'm confident we'll get a good statement," he added.

Trump's ascent to the White House has upended years of US-led pushes for more open global trade and lower tariffs.

One of his first moves after taking office was to pull US support for the Trans Pacific Partnership (TPP) trade deal, an American-led initiative between 12 Pacific countries that deliberately excluded Washington's big regional rival China.

The remaining 11 countries have since struggled to reboot the deal and China has since portrayed itself as the world's global free trade leader, pushing its own version of TPP.