Donald Trump has accused Twitter of interfering in the 2020 presidential elections and “completely stifling free speech” after the social media site slapped a fact-checking button on the US President’s account.

Twitter made the decision on Tuesday, warning readers Trump’s claims about mail-in ballots were false and had been debunked by fact checkers.

The blue exclamation mark notification prompted readers to "get the facts about mail-in ballots" and directed them to a page with news articles and information from fact-checkers about the claims.

Trump censored by Twitter for first time

"Trump makes unsubstantiated claim that mail-in ballots will lead to voter fraud," a headline at the top of the page said.

Trump, an avid user of social media, had claimed in tweets earlier in the day that mail-in ballots would be "substantially fraudulent" and result in a "rigged election." He also singled out the governor of California over the issue, although the state is not the only one to use mail-in ballots.

Twitter confirmed this was the first time it had applied a label to a tweet by the president under its new "misleading information" policy, introduced earlier in the month.