US President Donald Trump has delivered a primetime address in which he accused China of interfering in the 2020 election and alleged "shocking vulnerabilities" in American voting systems.

Trump, who spoke from the White House on Thursday, has repeatedly made unsubstantiated claims about voter fraud and foreign meddling in the 2020 election, which he lost to Joe Biden.

In the half-hour speech, delivered three months before the midterm elections, he said he had declassified hundreds of intelligence files which supported his claims that Beijing had tried to sway the election in Biden's favour.

The US intelligence community has previously concluded China did not interfere in the 2020 election.

In response to his speech, China's foreign ministry strongly denied the allegations of Chinese meddling in the 2020 presidential election, saying they were "entirely fabricated".

Trump's claims are "malicious smears" which have "long been proven to be groundless", foreign ministry spokesman Lin Jian said.

Trump spoke in front of several members of his top team as he gave his address, but journalists were unable to put questions to the president.

In his remarks, he accused China of the "illicit acquisition" of 220 million voter files including personal information.

Trump said voter data in 18 states was "bought, stolen or hacked by China" and accused "those responsible for sounding the alarm" of not disclosing the discovery to government officials or Congress.

A lot of voter data is publicly available and Trump did not in his speech present any evidence that China had used this information to alter voting systems or to influence election outcomes.

Hundreds of pages of intelligence documents were released by the White House during Trump's address, many of them heavily redacted. The BBC is in the process of reviewing them.

Democrats, meanwhile, accused Trump of attempting to sow doubts about the security of the upcoming November midterms which will decide control of Congress for the remainder of his presidency.

"Let's be clear - in America, voters choose their leaders, not the other way around," top Senate Democrat Chuck Schumer posted on social media after the speech.

"Democrats will fight like hell to make sure every American voter can cast their ballot freely, without obstruction or interference from Donald Trump," he added.

The president's comments contradict previous US intelligence assessments. A 2021 report by the US National Intelligence Council said it had "high confidence" that China did not interfere in the 2020 presidential election.

"We assess that China did not deploy interference efforts and considered but did not deploy influence efforts intended to change the outcome of the US presidential election," the report stated.

It said this was probably because China "did not view either election outcome as being advantageous enough for China to risk blowback if caught".

Trump delivered the White House address after the release of a new poll from Washington Post-Ipsos, which indicated his approval rating had dropped to 37% with many voters pessimistic about the cost of living and the ongoing war with Iran.

Elsewhere in the speech, the president alleged that US voting machines are "extremely exposed" to interference by foreign adversaries, including Russia, China and Iran.

Shortcomings of US election infrastructure have been well-documented. Some were addressed after the 2016 election which Trump won, after the US intelligence community found that Russia had engaged in a concerted election meddling campaign that included hacking, social media influencing and funding of on-the-ground electioneering activities.

During the address, Trump also alleged that a state investigation by Michigan law enforcement discovered a voter registration fraud scheme by a Democratic-affiliated group, but was constrained by the FBI from taking action before the statute of limitations expired.

"It was pay, play and cheat," he said, although he provided no evidence of votes or tabulations being changed or voting machines hacked.

Separately, Trump said that the Department of Homeland Security had identified 278,000 non-citizens were registered to vote. He did not say whether any of those people had voted or had an impact on any election outcome.

At the end of his speech, Trump again called for the passing the of the SAVE America Act, which bans most mail voting, requires proof of citizenship for voter registration and photo ID to cast a ballot.

That legislation has been stalled in the Senate for months.

Trump encouraged Americans to urge their representatives in Congress to support its passage, but unless Republicans are also willing to abandon longstanding Senate procedures such efforts are almost certainly doomed.

The speech is likely to do little to quell the concerns of Democrats that Trump is attempting to call into question the security of the upcoming midterms and the 2028 presidential election.

"He wants you to lose confidence in our electoral system so you stay home this November," former Vice-President Kamala Harris wrote on X moments before Trump's remarks.

In his address Trump also attacked media outlets, including ABC, NBC and CNN, who did not run his speech live on TV, saying they should have their broadcast licences revoked.

After the 2020 election, Trump and his allies launched dozens of unsuccessful legal challenges to contest Joe Biden's win and no evidence of widespread fraud was found.

The US Cybersecurity and Infrastructure Security Agency called the 2020 election "the most secure in American history" and that no voting systems were compromised.