Police in riot gear worked to separate a growing crowd of Donald Trump protesters from supporters still trying to get into the packed Pacific Amphitheatre minutes before the Republican presidential candidate was scheduled to make his first primary campaign speech in California.

About three dozen anti-Trump demonstrators marched toward Trump supporters waiting in line at OC Fair & Event Center in Costa Mesa. Sheriff’s deputies acted quickly – as both sides shouted slurs and profanity – creating a barrier between the sides with officers on horseback.

Roughly a dozen backup deputies were called in to further separate the two sides as the anti-Trump contingent appeared to steadily walk forward and push back the horses. Those on the pro-Trump side were told to stand on the sidewalk.

“It was scary,” Chelsea Rogers, 25, a Costa Mesa cosmetologist who came to the rally with her 16-year-old brother and who supports Trump. “If it gets any crazier, I don’t know what the police will do.”

On the anti-Trump side, Katrina Mendoza, 22, an Orange Coast college student, quickly walked away from the crowds as her friends urged her not to go back to the protest.

“A lady tried to hit me,” Mendoza said. “She called me disgusting and told me to go back to my country. But I was born here.”

The atmosphere outside became increasingly tense as both sides continued shouting obscenities, with hundreds of protesters cordoned off in a portion of the parking lot.

Inside the amphitheater, the atmosphere more closely resembled a rock concert, with a huge American flag hanging behind the speaker’s podium and Elton John music blasting from loudspeakers.

The theater was about 85 percent full near the 7 p.m. scheduled start time, with more people still trying to get in as the crowd got ready for Trump to take the stage. As of 7:30, Trump still had not spoken.

“Mr. Trump is not going to do this by himself,”said Rancho Santa Margarita Mayor Tony Beall, warming up the crowd. “We are an Army. Together, we can do anything.”

He continued, “Is America worth fighting for?”

The crowd cheered.

“Is Donald Trump the one who’s going to squash Hillary Clinton in a landslide?”

The crowd cheered louder.

An announcer over the loudspeaker instructed protesters to stay outside in a designated area. And he told Trump supporters they should not touch protesters.

Secret Service agents escorted one man out as he filmed the crowd with a hand-held camera. It wasn’t clear what triggered his removal. Agents took a T-shirt deriding Trump with an expletive from another man.

Meanwhile, many people in the crowd were talking politics amongst themselves.

David Rose, 58, of Cypress, a lifelong Republican, said Trump represents “average Americans” and has the business acumen to run the country.

“He’s independent, not beholden to special interest and has had success running large organizations,” Rose said.

There appeared to be few Trump protesters inside the arena. But one, Gerardo Ramirez, 20, of Santa Ana said he “hates” Trump.