UPDATED April 29, 2016, 2 p.m. PT with arrest figures.

Rowdy protests prior to Donald Trump's Southern California rally Thursday evening devolved into all-out rage when the GOP front-runner finished speaking to a capacity crowd at the Orange County fairgrounds.

Hundreds of protesters swarmed the streets outside the sprawling Costa Mesa venue. Some smashed the rear window of a police car, while a few jumped atop the vehicle. Protesters unsuccessfully tried to flip the car before authorities intervened. An anti-Trump crowd temporarily blocked a freeway onramp, bringing benches and chairs to sit on.

Back window has been smashed out of a Costa Mesa police cruiser. Protester: "I think Donald Trump did it!" pic.twitter.com/FTj4JoiAdN — Matt Pearce (@mattdpearce) April 29, 2016

Video: Anti-Trump protesters try to flip police car in Costa Mesa, Calif - KABC via @breaking https://t.co/X60PUcIchn — helga silva (@helgasilvaNOW) April 29, 2016

Images and video of the protest flooded social media as "Costa Mesa," "Orange County," #TrumpOC and #TrumpRally trended on Twitter throughout the evening.

The police car, from a few minutes ago pic.twitter.com/o2ChcXadT3 — Jim Dalrymple II (@JimDalrympleII) April 29, 2016

They've now set up benches at the on ramp to 55 Fwy. #CostaMesa pic.twitter.com/sOd2JblUZa — Ruben Vives (@LATvives) April 29, 2016

Protesters now Newport Blvd and Fair drive where protesters watch vehicles doing donuts. #CostaMesa pic.twitter.com/fHpcTOVlGb — Ruben Vives (@LATvives) April 29, 2016

Car burning tires, honking and chanting outside of Vanguard University in #CostaMesa pic.twitter.com/HgKUzOMLXD — Ruben Vives (@LATvives) April 29, 2016

CostaMesa Demonstrators have moved east of Fairview on Fair Dr. PD holding the line at Fairview @FOXLA pic.twitter.com/Z6ZBdJz1Yo — Kevin Takumi (@KevinTakumi) April 29, 2016

About 20 people were arrested and there were no major injuries, according to the Orange County Sheriff's Department. Authorities attempted to break up crowds along city streets throughout the night, tackling pockets as they formed. The protesters dispersed around 11 p.m. PT.

Post Trump Rally protests in street at Fair&Fairview CM- law enforcement attempting to disperse crowd. No arrests pic.twitter.com/aJT4HGzepK — OC Sheriff, CA (@OCSD) April 29, 2016

Just witnessed 3 arrests as police ask pedestrians to disperse & move out road: pic.twitter.com/wCuqFgrdxh — Jeremy Diamond (@JDiamond1) April 29, 2016

Police have declared Trump protest as unlawful assembly. Protestors told to disperse pic.twitter.com/GDpA4bCdjA — Steve Angeles (@StevieAngeles) April 29, 2016

It's not unusual for Trump rallies to turn violent. They have in Chicago, Wisconsin, Florida and elsewhere. And in Orange County, which is more than a third Latino, according to the U.S. Census Bureau, Trump's anti-immigrant rhetoric lit a match. Protesters could be seen holding Mexican flags and signs that said "Build A Wall Around Trump."

Arianna Perez, 19, with the sign: "We could be peaceful & do things different, but we wouldn't get our voice heard." pic.twitter.com/xjkDOUY3et — Matt Pearce (@mattdpearce) April 29, 2016

Even before Trump took the stage in front of thousands to talk his usual fare about building a wall between the U.S. and Mexico and making America great again, his supporters and detractors faced off. Punches were thrown, expletives were shouted. Authorities in riot gear and mounted police had to break up the two sides, forming a barrier between them.

Punches thrown at #Trump rally in Costa Mesa pic.twitter.com/SAYRYKkOfD — Maya Sugarman (@mayasugarman) April 29, 2016

Later in the evening, fighting between the pro and anti-Trump crowd picked up again, with a handful of supporters intentionally jamming their cars into protest crowds. One Trump supporter's face was bloodied after being punched.

A @realDonaldTrump supporter just got punched in the face as a scuffle broke out in the street: pic.twitter.com/3h3Fllm3V3 — Jeremy Diamond (@JDiamond1) April 29, 2016

It wasn't all violent, though, at one point, demonstrators line danced.

No words for protestors line dancing outside the Trump rally in Costa Mesa. pic.twitter.com/R2izVHTJEK — Nidia Becerra (@nidia_b) April 29, 2016

From earlier, protesters dancing pic.twitter.com/ObD6ToEtaY — Jim Dalrymple II (@JimDalrympleII) April 29, 2016

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