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Hundreds of protesters gathered outside a California hotel where Donald Trump spoke Friday, forcing the GOP front-runner to make a back door entrance he equated to "crossing the border."

“That is not the easiest entrance I’ve ever made,” Trump told the California GOP convention in Burlingame, south of San Francisco. And on Saturday, he took to Twitter to call the demonstrators “thugs and criminals,” adding that “They should be dealt with strongly by law enforcement!”

The "protesters" in California were thugs and criminals. Many are professionals. They should be dealt with strongly by law enforcement! — Donald J. Trump (@realDonaldTrump) April 30, 2016

Coverage of the protests captured Trump and his security detail traversing unkempt terrain in order to enter the venue without confrontation.

“We went under a fence and through a fence,” Trump added. “Oh boy, it felt like I was crossing the border, actually. I was crossing the border, but I got here.”

Several hundred protesters gathered outside the hotel in Burlingame, California. Some carried Mexican flags and held signs protesting Trump's controversial plan to build a wall along the U.S.-Mexico border to prevent illegal immigration.

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Though the protests were mostly peaceful, earlier Friday a Trump supporter was accosted as he tried to enter the convention. Chris Conway said he was surrounded by protesters and was punched and kicked as he tried to enter the convention wearing a "Make America Great Again" cap. Some shouted "racist!" at Conway.

"These guys felt free to hit me in my hometown of Burlingame; I don't stand for that," Conway said.

Later, a group overran police barricades and reached an entrance to the hotel, chanting slogans and holding signs outside the doors. Protesters hung a banner that read "Dump Trump" from an overhead walkway near the entrance.

Shortly before Trump was scheduled to arrive, a small group broke down barricades and rushed the hotel. That group burst through a police line at the street entrance and made their way to building, while others tried to clamber over hedges — with several becoming stuck.

A large group of police wearing helmets and carrying batons shoved the group back to the rest of the crowd and formed a line at the street entrance.

"He’s been inciting violence against black people and brown people and Muslim people," one protester said of Trump. She added she and others had no plans to leave the demonstration.

"I think we should be interrupting the convention and make sure that Trump does not make the stage today," she said. Trump gave his speech without incident and left through a side entrance without being stopped or even apparently largely noticed by protesters.

A protester was taken down by police. This came suddenly, after it seemed like things had calmed down. pic.twitter.com/C9XTxV6IeC — Ali Vitali (@alivitali) April 29, 2016

The protesters remained even though Trump had left. More than an hour after Trump departed, one person was seen being dragged off and handcuffed as a diminished crowd remained near an entrance to the building grounds, at times yelling at police.

By around 3 p.m. local time (6 p.m. ET) most of the crowds near the convention had dispersed.

Crowd now chanting at police "who do you serve?" pic.twitter.com/ryTrtQJO9J — Ali Vitali (@alivitali) April 29, 2016

One night earlier police arrested 17 people outside a Trump rally in Costa Mesa, California, south of Los Angeles. It was the worst violence associated with a Trump rally since his cancellation of a campaign event in Chicago.

In Costa Mesa, members of the crowd broke the windows of a police car and tried to flip the vehicle over. Five police vehicles in all were damaged, police said. A man identified as a Trump supporter was seen bleeding from a head injury after a confrontation with members of the crowd.

One Costa Mesa police officer was struck in the head by a rock thrown by a person identified as a protester; the officer was protected by his helmet.

Costa Mesa police on Friday identified those arrested Thursday. Most were between the ages of 18 and their early 20s, police said.