Emerging nations, which represent about half the world's population and 40 percent of global economic output, are set to unite over "serious concerns" about US import tariffs, according to a draft summit statement obtained by AFP.

Since coming to office in January, Trump has threatened allies and rivals alike with a slew of punitive duties.

His latest salvo comes in the form of letters informing trading partners of new tariff rates that will soon enter into force.

The draft summit declaration does not mention the United States or its president by name. 

But it is a clear political shot directed at Washington from 11 emerging nations, including Brazil, Russia, India, China and South Africa. 

"We voice serious concerns about the rise of unilateral tariff and non-tariff measures which distort trade and are inconsistent with WTO (World Trade Organization) rules," the draft text says. 

It warns that such measures "threaten to further reduce global trade" and are "affecting the prospects for global economic development."

Conceived two decades ago as a forum for fast-growing economies, the BRICS have come to be seen as a Chinese-driven counterbalance to Western power. 

But the two-day summit's political punch will be depleted by the absence of China's Xi Jinping, who is skipping the annual meeting for the first time in his 12 years as president. 

"I expect there will be speculation about the reasons for Xi's absence," said Ryan Hass, a former China director at the US National Security Council who is now with the Brookings Institution think tank.

"The simplest explanation may hold the most explanatory power. Xi recently hosted Lula in Beijing," said Hass.

The Chinese leader will not be the only notable absentee. War crime-indicted Russian President Vladimir Putin is also opting to stay away, but will participate via video link, according to the Kremlin.

Hass said Putin's non-attendance and the fact that Indian Prime Minister Narendra Modi will be a guest of honor in Brazil could also be factors in Xi's absence.

"Xi does not want to appear upstaged by Modi," who will receive a state lunch, he said.

"I expect Xi's decision to delegate attendance to Premier Li (Qiang) rests amidst these factors."

Still, the Xi no-show is a blow to host President Luiz Inacio Lula da Silva, who wants Brazil to play a bigger role on the world stage.

In the year to November 2025, Brazil will have hosted a G20 summit, a BRICS summit, and COP30 international climate talks, all before heading into fiercely contested presidential elections next year, in which he is expected to run.

Iran's President Masoud Pezeshkian, whose nation is still reeling from a 12-day conflict with Israel, is also skipping the meeting. 

A source familiar with the negotiations said the BRICS countries were divided over how to respond to the wars in Gaza and between Iran and Israel. 

Iranian negotiators were pushing for a tougher collective stance that goes beyond referencing the need for the creation of a Palestinian state and for disputes to be resolved peacefully.

But one diplomatic source said the text would give the "same message" that BRICS delivered in June when Iran was being bombed by Israel and the United States, expressing "concern."

Artificial intelligence and health will also be on the agenda at the summit.

Original members of the bloc Brazil, Russia, India, and China have been joined by South Africa and, more recently, by Saudi Arabia, Iran, the United Arab Emirates, Egypt, Ethiopia and Indonesia.