The announcement, which came amid large protests both inside and outside the event at The University of Illinois, comes amid heightened concerns about violence at the GOP front-runner’s rallies and four days before Illinois holds its Republican primary.

Hundreds of demonstrators packed into an arena, breaking out into protest even before Trump had showed up. At least five sections in the arena were filled with protesters.

“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.”

Several fistfights between Trump supporters and protesters could be seen after the announcement, as a large contingent of Chicago police officers moved in to restore order.

Supporters of Trump still inside chanted “We want Trump” after the event was canceled. Protesters, meanwhile, shouted “We shut s*** down” and “We stumped Trump.” Others chanted “Bernie” as supporters whipped out Bernie Sanders campaign signs.

Some protesters were being detained and forcefully carried out.

Maria Hernandez, a 25-year-old community organizer, broke out into dance as a Trump campaign staffer announced that the rally had been canceled.

“I’ve never been more proud of my city,” Hernandez told CNN.

Hernandez, who came out to protest Trump, said the Republican front-runner’s immigration policies, as well as racial divisions in her city, pushed her to show up and protest Trump’s planned event

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“I’m protesting because I’m black and Mexican and I’m not sure where he wants to deport me to, but I deal with racism daily in Chicago and I’ve had enough,” she said.

One Trump supporter said he was “disappointed” that the event was postponed.

“Protesters have won now,” Marlin Patrick, 55, told CNN. “We just feel as if the protesters have taken over.”

Debi Patrick, a 53-year-old Trump supporter who lives outside Chicago, said there should have been more security planned for the event, but said she didn’t blame Trump for the atmosphere at the rallies, saying people are responsible for their own behavior. Asked if she would still vote for Trump on Tuesday, she said, “Absolutely, more than ever.”

But, Patrick said, “This is scaring the hell out of me, trying to leave here.”

Chicago police spokesman Anthony Guglielmi told CNN that there were no reports of injuries or arrests at the event. He added that attendees were exiting the rally and appeared to be civil.

Guglielmi added that the decision to postpone the event was not made by Chicago police.

A crowd of protesters outside the rally site had been steadily growing throughout the afternoon. Earlier Friday, 32 people were arrested in protests both inside and outside Trump’s rally at the Peabody Opera House in St. Louis, police said. Thirty-one people were charged with disturbing the peace, and one was charged with third-degree assault. St. Louis police declined to provide further details.

Soon after the event was postponed, scores of protesters — a racial mixture of whites and blacks, Hispanics and Asians — spilled out into the streets near the university, which is located in the city’s downtown.

Dozens of protesters gathered outside a parking garage adjacent to the arena, where police set up a human barricade to allow supporters to go to their cars and leave. More than a dozen police officers on horseback were there.

“Let’s go, let’s go,” one Chicago police officer told Trump supporters in a truck. “Go home.”

One supporter, who didn’t give his name as he drove out, said the situation was dangerous and that he felt unsafe as protesters shouted at his car.

At one point, a man on the third floor of the garage leaned over the edge and shouted at protesters, “I don’t support Trump.”

A protester responded, “You f***ing neo-Nazi prick, come down here.”

Aureliano Rivas, 18, a Mexican-American high school student from Chicago, told CNN he was protesting because “we have to stand our ground.”

“We shouldn’t let racism happen like this,” said Rivas, who was shouting “F*** Trump” as Trump supporters drove out of the garage. In response, Rivas said, supporters were flipping him off.

Asked what he would tell a Trump supporter, Rivas said, “This is wrong. You shouldn’t support someone who is racist.”

Speaking to MSNBC’s Chris Matthews after the event, Trump said he deplored the violence and said it signaled something broader about society.

“You can’t even have a rally in a major city in this country anymore without violence or potential violence. And I didn’t want to see the real violence, and that’s why we called it off,” Trump said.

Trump said he recognized that both sides were angry, but was largely unsympathetic to the protesters’ concerns.

“You have people that are very, very upset about what’s happening with our country as a country, and you have other people who don’t just feel right about things,” Trump said.

Later, as protests outside the arena continued, Trump tweeted that he had “just got off phone with the great people of Guam,” which holds a Republican convention on Saturday to elect delegates.

“I just got off the phone with the great people of Guam! Thank you for your support! #VoteTrump today! #Trump2016.”

Protests and racial tensions have recently escalated at Trump rallies. On Thursday, a man attending a Trump rally this week was charged with assault after he allegedly sucker-punched a black protester being led out of a Trump event.

Last fall, Trump said a Black Lives Matter protester maybe “should have been roughed up.” And despite an announcement at the start of his rallies urging protesters not to be violent toward protesters, Trump in February urged his supporters to “knock the crap out of” anybody “getting ready to throw a tomato” and vowed to pay for their legal fees should they face charges.

“Knock the crap out of them, would you? Seriously. OK? Just knock the hell — I promise you, I will pay for the legal fees. I promise, I promise,” Trump said.

And Trump also said he personally wanted to punch a protester “in the face” during a rally in February.

But at CNN’s Republican debate on Thursday, Trump insisted that he did not support violence at his events.

“I certainly do not condone that at all,” Trump said, adding, “We have some protesters who are bad dudes. They have done bad things.”