Marchers took to the streets at the same time a military parade rolled through Washington, DC, to mark the 250th anniversary of the US Army, which also happened to be Trump’s 79th birthday.

Among those who joined the protest in Los Angeles was talk show host Jimmy Kimmel.

Kimmel took to Instagram to praise the “peaceful” demonstration he attended in South Bay, a south-west region of LA.

“A huge, inspiring and yes – peaceful – turnout in the South Bay. I met many people who love this country and still believe it to be a force for good,” Kimmel, who wore a “Make America Good Again!” shirt, posted on Instagram.

“I am grateful to see so many Americans take action to stand up for our friends and neighbours, most of all, my parents. 

“I know how fortunate I am to have been born into a family that taught me to care about others and that the most important words ever spoken are “Love one another.” It really is as simple as that.”

Kung Fu Panda star Jack Black was also spotted by protesters walking down the street during another No Kings march in Los Angeles.

It remains unclear if Black was joining the protest or happened to be walking past at the same time.

Footage shared on TikTok shows the actor crossing the road and being accosted by fans.

Over on the east coast, A-listers Mark Ruffalo and Susan Sarandon were seen joining protests in New York City.

Several other celebrities took to Instagram to share images of themselves holding signs, including Anna Kendrick, Julia Louis-Dreyfus, Marisa Tomei and Kerry Washington.

Seinfeld star Louis-Dreyfus held a sign which read: “The only monarch I like is a butterfly.”

Tensions boil at ‘No Kings’ protests 

Demonstrators poured onto streets and parks to decry the Republican president as a dictator or would-be king, overshadowing celebrations for the 250th anniversary of the US Army – and what is also Trump’s birthday.

Huge, boisterous crowds marched in New York, Denver, Chicago, Houston and Los Angeles, some behind “no kings” banners.

Atlanta’s 5000-capacity event quickly reached its limit, with thousands more gathered outside barriers to hear speakers in front of the state Capitol.

In some places, organisers handed out little American flags while others flew their flags upside down, a sign of distress. Mexican flags, which have become a fixture of the Los Angeles protests against immigration raids, also made an appearance at some demonstrations on Saturday.