Tangled in an escalating trade dispute with the United States, China's top diplomat insisted on Friday that his country "will not be blackmailed" or bow to pressure.

"Protectionism will only hurt oneself, and unilateral moves will bring damage to all," Foreign Minister Wang Yi told the UN General Assembly gathering of world leaders.

He spoke in a week when Washington and Beijing both raised tariffs on each other's products, and US President Donald Trump alleged that China is meddling in the upcoming US midterm elections because it opposes his trade policies.

China denied the claim, and Wang did not address the issue in his speech.

"China will not be blackmailed or yield to pressure," Wang said, describing his country's moves as defending not just its own interests but the system of global trade.

Noting that China spent more than a decade negotiating its membership in that system, he said his country has fulfilled its promises and is committed to resolving disputes within the framework of the World Trade Organization.

"State-to-state relations must be based on credibility, not on wilful revocation of commitments," he said.

Despite often touting his good personal relations with Chinese President Xi Jinping, Trump criticised China for not opening its markets and says such an approach is unacceptable.

Russia, which also has vigorously denied accusations of meddling in US elections, was due to speak later on Friday.

China has been asserting itself on the world stage under Xi, though it continually stands by a foreign policy of non-interference in the affairs of other countries. It has long used that policy to rebuke other countries that criticise its record on human rights.

The country has come under increased criticism as its global profile has risen and its economic interests and accompanying political clout have spread from Asia to Africa, Latin America and the Middle East.

Besides China's clash with the Trump administration, some Africans have protested what they say is an attempted Chinese takeover of their countries.

Trump increased tariffs on Monday on USD 200 billion of Chinese goods. 

Beijing responded by imposing penalties on USD 60 billion of American products. That was on top of an earlier duty increase by both sides on USD 50 billion of each other's goods.

The US said China steals or pressures foreign companies to hand over technology, and that Beijing's plans for state-led development of global competitors in robotics and other technologies violate its market-opening obligations and might erode US industrial leadership.

China has accused the Trump administration of bullying.

A Chinese official said on Tuesday that China cannot hold talks on ending the trade dispute while the US "holds a knife" to Beijing's throat by hiking tariffs.

The next day, Trump stunned other members of the Security Council by saying that China was meddling in the midterm elections because it opposes his tough trade policies.

When questioned by reporters, Trump said there was "plenty" of evidence but didn't immediately provide details. Instead, he zeroed in on China's efforts to flood the US with ads and statements against Trump's billions of dollars in tariffs on Chinese goods.

Beijing was quick to respond, urging Washington to stop slandering China and claiming that the Chinese government does not interfere in other countries' internal affairs.

Russia, meanwhile, has been the focus of a special counsel investigation into interference in the 2016 election, a probe that Trump has lambasted as a political "witch hunt."

Russia is expected to use its turn at the podium to promote itself as a counterweight to US influence in areas from the Middle East to Venezuela and the Korean peninsula.

Russian Foreign Minister Sergey Lavrov has held a flurry of individual meetings with other countries at the UN this week and vociferously defended Russia's strategies in meetings at the Security Council.

Syria has been a running theme as Moscow seeks to manage the end of the civil war and ensure a long-term foothold in the region.

As a long time ally of Syrian President Bashar Assad, Russia wants Western aid for financing postwar reconstruction while also maintaining its upper hand in discussions about the country's political future.

Lavrov promised wide-ranging Russian aid in a meeting with embattled Venezuelan President Nicolas Maduro, who faces international condemnation, increasing US sanctions and fears of a possible US intervention.

Seeking to maintain leverage in discussions on North Korea's denuclearization efforts, Lavrov met with North Korea's foreign minister the same day that Ri Yong Ho met with US Secretary of State Mike Pompeo.

Lavrov also offered support to Palestinian President Mahmoud Abbas right after Abbas slammed the US decision to recognize Jerusalem as Israel's capital.

Other scheduled General Assembly speakers on Friday include the leaders or Malaysia, Germany, Iraq and South Sudan.