As the military presence ramped up in Los Angeles, communities are preparing for the largest protests against Trump since he took office.

About 50 U.S. Marines squared off against hundreds of protesters in front of a federal building in downtown Los Angeles on Saturday, with the crowd yelling in unison for them to go home.

After a week of watching a fun-house-mirror version of their city in global media, thousands of Los Angeles residents took to the streets on Saturday.

The Marines wearing combat gear and carrying rifles are taking over some posts from National Guard members who were deployed to the city after the protests erupted last week. Those protests sparked dozens more over several days around the country, with some leading to clashes with police and hundreds of arrests.

About 200 Marines have moved into Los Angeles and will protect federal property, personnel, the commander in charge says. Maj. Gen. Scott Sherman, commander of Task Force 51 who is overseeing the 4,700 troops deployed,

Marines carried out the first known detainment in L.A. — the latest provocation in Trump’s militarized answer to immigration enforcement.

Roughly 700 Marines from the Twentynine Palms base have been mobilized in response to protests and unrest in Los Angeles.

The Pentagon plans to deploy 700 Marines to Los Angeles to help National Guard members respond to mass immigration protests.

What Happened: According to a Reuters report, U.S. Marines temporarily detained a civilian in Los Angeles on Friday. This marks the first known instance of active-duty troops, deployed by President Donald Trump, detaining a civilian in the city.

United States Army North confirmed to ABC News that Marines at the Wilshire Federal Building have made the first temporary detention among the troops sent to Los Angeles on Friday.