Actor Robert De Niro made a surprise appearance in New York City on Tuesday outside the Manhattan courtroom where Donald Trump's hush money trial is coming to a close, issuing a stark warning to Americans watching along. 

The actor slammed the former president as a "danger" to the United States.

"I hope this new ad campaign reaches outside the bubble to remind supporters of what a danger he is to our lives. This is not a threat. This is our reality. And that's why I've joined the Biden-Harris campaign," said De Niro.

Biden's campaign communications director, Michael Tyler, was on site alongside De Niro.

"Trump poses a unique and growing threat to our fundamental rights and freedoms, our very democracy, and our economy." Tyler said, highlighting the anticipated June 27th debate between Biden and Trump.

Meanwhile, De Niro argued in front of shouting protesters, declaring Trump does not "belong" in New York City, as reported by Fox News.

"Donald Trump wants to destroy not only the city but the country. And eventually he could destroy the world," he stated.

The actor said he owes the city of New York a lot, explaining, "That's why it's so weird that Donald Trump is just across the street because he doesn't belong in my city."

"We New Yorkers used to tolerate him when he was just another grubby real estate hustler masquerading as a big shot," De Niro added.

Just recently, the actor lent his voice to a Biden-Harris campaign ad dubbed "Snapped," which portrays Trump as an out-of-control, wannabe dictator whose goal is to terminate the Constitution.

The Trump campaign also organized a press conference Tuesday, where campaign senior adviser Jason Miller attacked De Niro as a "washed-up actor."

Nearing the end of his trial, Trump faces 34 counts of falsifying business records.

"This is a very dangerous day for America. It's a very sad day," Trump said in remarks to the media before heading into the Manhattan courtroom Tuesday morning.