Donald Trump has led Twitter to use a new "manipulated media" for the first ever time, after sharing a misleading video of Joe Biden.

The video appears to show Mr Biden stumbling in a speech and apparently suggesting "we can only re-elect Donald Trump". But it was cut-off before Biden was able to complete his sentence, which was actually a call for unity.

Twitter chose to censure Trump's team over the video, attaching the new tag to the post. But Facebook is still allowing it to be shared as normal.

The video has been viewed millions of times on each site.

The video, which was posted on Saturday by White House social media director Dan Scavino, showed Biden stumbling on a speech in Kansas City, Missouri, in which he said the words "Excuse me. We can only re-elect Donald Trump."

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Biden's full sentence, which was cut off by the clip, was "Excuse me. We can only re-elect Donald Trump if in fact we get engaged in this circular firing squad here. It's gotta be a positive campaign so join us."

Twitter implemented its new policy, which labels tweets with manipulated or synthetic media such as deepfakes or more manually edited videos, on 5 March.

However, Twitter's new label was not showing for all users.

The tag was applied on Sunday afternoon, but Twitter said it was not showing when people searched for the tweet or clicked into it, only when it was seen in timelines. A Twitter spokesman said the company was working on a fix.

"The video was NOT manipulated," said Scavino in a later tweet.

Social media companies are under pressure to police misleading or false information on their platforms ahead of the U.S. presidential election in November, in which Biden and Senator Bernie Sanders are vying to be the Democratic nominee to oust Republican President Trump.

The video, which had about 5.8 million views on Twitter at the time of writing, was also posted on Scavino's Facebook page, where it had about 1 million views.

The Biden campaign slammed Facebook Inc. for showing the video on its platforms without labels.

"Facebook won't say it, but it is apparent to all who have examined their conduct and policies: they care first and foremost about money and, to that end, are willing to serve as one of the world's most effective mediums for the spread of vile lies," said Greg Schultz, Biden's campaign manager.

Facebook did not immediately respond to a request for comment.