US presidential candidate Donald Trump postponed a rally scheduled for Friday night in Chicago after the event turned into a chaotic scene at the University of Illinois-Chicago, with the thousands of attendees split into opposing camps of supporters of the Republican front-runner and protesters against his candidacy.

Fights broke out after a Trump staffer took to the stage nearly a half hour after the rally was slated to begin and told the crowd that the event would be postponed due to safety warnings from law enforcement.

"Mr. Trump just arrived in Chicago and after meeting with law enforcement has determined that for the safety of all of the tens of thousands of people that have gathered in and around the arena, tonight's rally will be postponed to another date," the Trump campaign said in a statement. "Thank you very much for your attendance and please go in peace."

A campaign statement issued slightly later said the event would be rescheduled, but did not offer details.

The crowd acted out after the announcement came over the loudspeaker, according to NBC Chicago.

Watch footage of the events in Chicago here:

Hundreds of protesters had gathered inside and outside of the event, multiple news outlets reported. Inside the now-cancelled rally, "at least five sections in the arena were filled with protesters," according to CNN. By 7:45pm, nearly two hours after the event was scheduled to start, protesters were reportedly blocking vehicles from exiting parking facilities near the arena where the event would have taken place.

After the announcement was made, protesters began to chant and cheer, inciting the ire of Trump's supporters. Scuffles broke out as signs were ripped from hands and police moved in to break up areas with the most serious conflicts.

Protesters inside appeared jubilant at times when not directly confronting Trump supporters. One group that had gathered started chanting the chorus from rapper Kendrick Lamar's anthem "Alright."

"We dumped Trump! We dumped Trump!" could be heard inside the pavilion where the event was held.

"We want Trump! We want Trump!" was yelled by an opposing group.

Chicago activists had spent the week leading up to the rally planning how to disrupt it.

One group, Showing Up for Racial Justice, coordinated with minority student groups on local campuses, using group email chains and messaging so that protesters could stay in constant communication.

One of the organizers, Nathaniel Lewis, a 25-year-old master's degree student in public health at the University of Illinois at Chicago, said he was shocked they succeeded in shutting the rally down.

"I'm happy, I'm at peace because we came together as a collective," Lewis told Reuters. "This is the last thing we expected to happen. It shows the power of unity."

Watch **_Trump's Guide to Dealing With Protesters**_

Trump called into all of the major cable news networks shortly after the violence broke out.

He emphasized to Fox News that the rally had merely been postponed, not canceled, but blamed the riot on anger all across the country at the direction the nation is heading in, citing the frustration of Americans who have gone for years without a pay increase.

"I am a unifier," Trump told Fox News. "President Obama has not been a unifier. He has been a divider. I'm a unifier. I'll bring people together."

Fellow Republican presidential contender Ted Cruz reacted to the incident during an interview on Hugh Hewitt's radio show. "There's no doubt that a candidate bears responsibility for the culture that is set from the top," he said, adding that he often engages with protesters when they are civil.

The Texas senator recalled his recent attack on the billionaire businessman for asking rally attendees to pledge loyalty to his campaign. Cruz said that, in contrast with Trump, he views protesters "with respect, not as potential subjects for a monarch."

Trump, speaking to MSNBC by telephone shortly after the postponed event, said he met with law enforcement after arriving in Chicago. Though he believed it would have been possible to move forward, he said he made the "wise decision" to postpone the rally to keep everyone safe.

Trump brushed off questions from MSNBC's Chris Matthews about whether such widespread disruptions were to be expected given the increasingly aggressive tenor of recent campaign events.

Trump said his supporters had planned for a peaceful rally and that it was derailed by the protesters.

"You can't even have a rally in a major city in this country anymore," Trump said. "Up until this point we've had no problem."

Trump told MSNBC he expected support for his candidacy would only increase.

Earlier in the day, at a rally in St. Louis, Missouri, Trump had been speaking for less than 10 minutes when protesters began interrupting him. The disruptions continued over the next hour as Trump urged security to "get them out."

"Can I be honest with you, it adds to the flavor, it's more exciting," Trump said of the disruptions. "Isn't this better than listening to a long boring speech?"

At some events, altercations have turned physical. In New Orleans last week, several protesters supporting the Black Lives Matter movement were dragged out as Trump shouted "get them." In Fayetteville, North Carolina, on Wednesday, protesters interrupted Trump's speech more than 16 times. One was punched as he was led from the arena.

Jedidiah Brown, 29, dashed onto the Chicago stage where Trump was expected to speak Friday and tore the campaign sign from the podium before police took him outside. He was not arrested.

"I was born and raised in Chicago so I felt it was my responsibility to let him know he's not welcome here," Brown said. "The message Trump is spreading all over the country, it doesn't work here."

Outside, Tess King, a 25-year-old social sciences and law student, was carrying a sign that said "Chicago Rejects Trump." King had tried to get into the rally but the event was canceled before she got in the door.

"I feel incredibly happy that in our city we managed, through peaceful expression, to make this happen," King told Reuters.

As the crowd began to trickle out, Josh Glaspie, 28, smoked a cigarette on a sidewalk strewn with discarded signs. Glaspie, an Army veteran who is trying to open a restaurant in Chicago, said he supports Trump.