The first of more than 2,500 planned protests against President Donald Trump has begun in New York City.

The organisers of the "No Kings" protests say that millions are expected to take part across the US. Trump allies have accused the protesters of being allied with the far-left Antifa movement, without evidence.

Republican governors in several US states have placed National Guard troops on standby.

Governors in Texas and Virginia have activated their state's National Guard troops, however it is unclear how visible the military presence will be.

The protests kicked off in New York City at 11:00 EST (16:00 GMT) and are expected to continue across the country throughout the day. Other major protests will occur in Washington DC, where Bernie Sanders is expected to be a keynote speaker, and Los Angeles.

The protest organisers say the protest will challenge Trump's "authoritarianism".

"The president thinks his rule is absolute," they say on their website.

"But in America, we don't have kings and we won't back down against chaos, corruption, and cruelty."

Throughout Europe, protesters have taken to the streets in Berlin, Madrid and Rome to show solidarity with their American counterparts.

In an interview with Fox News, set to air Sunday, but teased on Saturday, Trump appeared to address the upcoming rallies.

"A king! This is not an act," Trump said in a preview clip of the interview. "You know – they're referring to me as a king. 'I'm not a king.'"

Some Republicans have dubbed the protests "Hate America" rallies.

"We'll have to get the National Guard out," Kansas Senator Roger Marshall said ahead of the rallies, according to CNN.

"Hopefully it'll be peaceful. I doubt it."

Texas Governor Greg Abbott on Thursday activated the state's National Guard ahead of a protest scheduled in Austin, the state's capital.

He said the troops would be needed due to the "planned antifa-linked demonstration".

Democrats denounced the move, including the state's top Democrat Gene Wu, who argued: "Sending armed soldiers to suppress peaceful protests is what kings and dictators do — and Greg Abbott just proved he's one of them."

Virginia Governor Glenn Youngkin also ordered the state National Guard to be activated.

Among the celebrities expected to attend No Kings rallies are Jane Fonda, Kerry Washington, John Legend, Alan Cumming and John Leguizamo.