Exiting US President Joe Biden has let slip another awkward blunder - which coincides with the poignant anniversary of the 9/11 attacks.

Speaking to reporters outside the White House on September 10, the 81-year-old laid out his schedule in the coming hours, saying: "I'm going up to my grandaughter's birthday, in New York. Then we're going to watch the debate, then tomorrow I'm doing 9/11."

The President's poor choice of words provoked both sock and amusement online, with one user posting: "Gotta be honest until I saw that 'tomorrow I'm doing 9/11' clip just now I kind of forget Joe Biden was even alive."

An X account associated with Donald Trump's campaign for reelection shared the short clip, claiming: "This is the humiliating cognitive decline Kamala Harris COVERED UP."

Almost 3,000 people were killed in the September 11, 2001 attacks, when al-Qaida terrorists highjacked four commercial aircraft and crashed them into the twin towers of the World Trade Centre, the Pentagon and a field in Pennsylvania.

The forth plane had been heading for the US capital but came down in Shanksville after passengers and crew members attempted to storm the cockpit.

Biden's sloppy phrasing is the latest in a series of gaffes for the Democrat, who announced in July he wouldn't be running for a second term amid pressure from within his own party in the wake of a disastrous debate performance against Donald Trump.

It was the culmination of weeks of concern about his fitness for office, as he made a number of high-profile blunders - including introducing Ukrainian president Volodymyr Zelensky - whose country has been at war with Russia for more than two years - as "Vladimir Putin".

His comments came ahead of the Presidential debate between Kamala Harris - his Vice President and the Democratic candidate for 2024 - and Donald Trump.

We'll be bringing you the very latest updates, pictures and video on this breaking news story.

For the latest news and breaking news visit: /news

Stay up to date with all the big headlines, pictures, analysis, opinion and video on the stories that matter to you.

Follow our social media accounts here on facebook.com/DailyExpress and @daily_express