During a prime-time speech from the White House, Trump revived many of his longstanding claims that US elections were unreliable, citing newly declassified documents that he said revealed "shocking vulnerabilities".
But many of the documents appeared to fall far short of backing his assertions.
While Trump cast US elections as highly vulnerable, he did not provide evidence of any votes in 2020 that were altered or manipulated.
A Chinese foreign ministry spokesman on Friday called the accusations of Chinese interference "totally fabricated and a malicious smear".
"China has always adhered to the principle of non-interference in internal affairs and has had no interest in, nor has it ever interfered in, US elections," Lin Jian said during a regular media conference in Beijing, adding Trump's allegations "have long been proven to be sheer nonsense".
Trump used his remarks to again press fellow Republicans in Congress to pass legislation imposing new voter identification and citizenship requirements, despite established findings that voter fraud is rare.
The bill, known as the SAVE America Act, has stalled in the Senate amid fierce Democratic opposition.
The speech came as Trump and Republicans face the prospect of losing one or both chambers of Congress in November, with the president's approval rating weighed down by the unpopular Iran war and high energy prices.
Some Republican leaders have urged Trump to focus on issues that matter most to Americans, including high living costs, rather than the 2020 vote.
Trump briefly mentioned the war, saying the US was "winning big", and listed domestic accomplishments such as tax cuts and his immigration crackdown before turning to election security.
The president said he was declassifying information that showed China had illicitly acquired 220 million US voter files, including names, addresses and other data.
He asserted that members of the US intelligence community deliberately suppressed the extent of China's activities.
An unclassified 2021 US intelligence assessment found no indications any foreign actor attempted to or succeeded in altering "any technical aspect" of the 2020 presidential election, including voter registrations, ballots, tabulations or results.
That assessment was conducted under John Ratcliffe, then Trump's director of national intelligence and now his CIA director.
Trump has spent years raising doubts about electoral outcomes, falsely asserting that his 2020 loss to Democrat Joe Biden was rigged.
He has also advanced other false claims, including that mail-in balloting is rife with fraud, voting machines are untrustworthy and non-citizen voting is widespread.
Numerous courts and vote recounts found no evidence of large-scale fraud in the 2020 election.
Nevertheless, Trump's campaign has gained traction with his supporters.
A Reuters/Ipsos poll in April found 63 per cent of Republicans believe Trump's claim that the 2020 election was stolen.
Trump said his administration had uncovered more than 275,000 non-citizens registered to vote in just four states, but he provided no evidence that any had actually voted.
Studies have found that non-citizens casting ballots is exceedingly uncommon.
Trump also said the newly declassified documents would reveal serious weaknesses in election security.
But many either appeared inconsistent with that assertion or were unrelated to US election infrastructure:
One CIA document, prepared in June, concerned Venezuela's election, not America's.
"We assess that vote tabulation systems would be difficult to manipulate on a wide enough scale to compromise election results," another document said.
"Trump's shocking 'bombshells' about China are totally bogus," said Democratic senator Mark Warner, vice-chair of the Senate intelligence committee.
"The fact is our intelligence agencies unanimously agreed that China did not even try to change a single vote in the 2020 election."
