US President Donald Trump has issued an executive order seeking to strip social media giants, like Twitter, of legal immunity for content posted by users.

If this was enacted, the likes of Twitter and Facebook would become open to lawsuits and greatly increased government regulation.

Mr Trump - angered this week after Twitter tagged one of his tweets for the first time with a fact-check notice - said regulation was needed because the companies are no longer neutral forums but engaging in "political activism".

According to Mr Trump, such platforms have "unchecked power to censor, restrict ... virtually any form of communication between private citizens".

"We can't let that happen," he said, "especially when they go about doing what they're doing because they're doing things incorrectly, they have points of view."

The president's ire appeared especially focused on fact-checking services that big social media platforms have added in an effort to weed out rampant disinformation and so-called "fake news".

This, he said, made the companies into traditional publishers, therefore liable for whatever material they host.

"The choices that Twitter makes when it chooses to suppress ... editorial decisions pure and simple," he said.

"In those moments, Twitter ceases to be a neutral public platform and they become an editor with a viewpoint and I think we can say that about others also, whether you're looking at Google, whether you're looking at Facebook, perhaps others."

According to Mr Trump, his executive order aims to "uphold the free speech and rights of the American people".

However, before this could go into effect it will face strong political opposition and Mr Trump conceded it would get challenged in court.

Opponents say Mr Trump's aim is to tame the same social media platforms on which he is easily the biggest political presence in the country, cowing their attempts to reduce misinformation.

While Mr Trump complains that social media leaders are liberal-leaning, he enjoys an overwhelming presence on Twitter, Instagram and Facebook and other outlets for his streams of often factually incorrect posts and crude insults against opponents.

Asked why he would not just walk away from Twitter, where he has 80 million followers, Mr Trump said he would, except that he relies on the platform to bypass the traditional media, which he complained is unfair.

"There's so much fake news, it's disgraceful," he told the journalists covering him in the Oval Office.

Mr Trump even mused about his desire to see Twitter disappear altogether - if he had any way to make this happen.

"If it were able to be legally shut down, I'd do it," he said.

"In terms of presidential efforts to limit critical commentary about themselves, I think one would have to go back to the Sedition Act of 1798 - which made it illegal to say false things about the president and certain other public officials - to find an attack supposedly rooted in law by a president on any entity which comments or prints comments about public issues and public people," said First Amendment lawyer Floyd Abrams.

Others like Jack Balkin, a Yale University constitutional law professor, said: "The president is trying to frighten, coerce, scare, cajole social media companies to leave him alone and not do what Twitter has just done to him."

Still, Twitter's shares were down 4.4%. Facebook was down 1.7% and Google parent Alphabet Inc were up slightly.

Separately, Mr Trump said he will give a press conference tomorrow on China amid spiralling US-Chinese tensions over Hong Kong and the coronavirus fallout.

Mr Trump told reporters of his plan at an Oval Office meeting, but gave no specific details of what he would be announcing.

Fears that China will use a new law to end Hong Kong's freedom as a semi-autonomous territory have prompted expectations that Mr Trump plans to hit back, possibly signaling a wider confrontation between the two economic superpowers.