US President Donald Trump has accused China of attempting to interfere in the upcoming congressional elections, claiming the Chinese are motivated by opposition to his tough trade policy.

Mr Trump was speaking in front of world leaders while chairing the United Nations security council for the first time.

His accusation comes amid the ongoing special counsel investigation into Russia’s attempts to interfere in the 2016 US election, and concerns that the November elections could also be vulnerable.

“Regrettably, we found that China has been attempting to interfere in our upcoming 2018 election,” Mr Trump said on Wednesday.

“They do not want me or us to win because I am the first president ever to challenge China on trade.”

Asked later what evidence he had, Mr Trump replied, “plenty of evidence”, but did not provide any.

“They would like to see me not win because this is the first time ever that they’ve been confronted on trade,” he repeated.

“And we are winning and we’re winning big. And they can’t get involved with our elections.”

A Chinese delegate shrugged when he heard Mr Trump’s statement via translation in the general assembly.

China later denied Mr Trump’s accusation.

“We do not and will not interfere in any countries’ domestic affairs,” said foreign minister Wang Yi at the United Nations.

“We refuse to accept any unwarranted accusations against China, and we call on other countries to also observe the purposes of the UN charter and not interfere in other countries’ internal affairs.”

There is extensive evidence linking Russia to attempts to penetrate US elections systems and to influence US voters.

But with the American midterm elections less than two months away, US intelligence and election protection officials have not cited any specific, credible Chinese efforts.

Officials say China’s cyber-espionage operations targeting US defence and commerce have been formidable, however.

And Mr Trump’s claim comes amid an escalation of tensions between Washington and Beijing, spurred by their growing trade dispute.

Each imposed tariff increases on the other’s goods on Monday and Beijing accused the Trump administration of bullying.

-AAP