CHICAGO (AP) – Republican presidential candidate Donald Trump canceled one of his signature rallies on Friday, calling off the event in Chicago due to safety concerns after protesters packed into the arena where it was to take place.

The announcement that the billionaire businessman would postpone the rally until another day led a large portion of the crowd inside the University of Illinois at Chicago Pavilion to break out into raucous cheers. Meanwhile, supporters of the candidate started chanting “We want Trump! We want Trump!”

There were isolated physical confrontations between some members of the crowd after the event was canceled.

There was no sign of Trump inside the arena on the college campus, where dozens of UIC faculty and staff had petitioned university administrators to cancel the rally. They cited concerns it would create a “hostile and physically dangerous environment” for students.

Before the announcement the event wouldn’t take place, a handful of intense verbal clashes took place between Trump supporters and protesters as the crowd waited for his arrival. For the first time during his White House bid, the crowd appeared to be an equal mix of those eager to cheer on the real estate mogul and those overtly opposed to his candidacy.

When one African-American protester was escorted out before the event started, the crowd erupted into chants of “Let them stay!”

Veronica Kowalkowsky, an 18-year-old Trump supporter, said before the event started that she had no ill will toward the protesters – but didn’t think they felt the same way.

“I feel a lot of hate,” she said. “I haven’t said anything bad to anyone.”

Hours before the event was scheduled to start, hundreds of people lined up outside the arena at the University of Illinois at Chicago – a civil and immigrant rights organizing hub with large minority student populations. Trumpbackers were separated from an equally large crowd of anti-Trump protesters by a heavy police presence and barricades.

Some Trump supporters walking into the area chanted, “USA! USA!” and “Illegal is illegal.” One demonstrator shouted back, “Racist!”

One protester, 64-year-old Dede Rottman of Chicago, carried a placard that read: “Build a Wall Around Trump. I’ll Pay for it.”

However, 19-year-old Rusty Shackleford of Lombard, in line to attend the Trump rally, said he was there to “support the man who wants to make America great again.”

Chicago community activist Quo Vadis said hundreds of protesters had positioned themselves in groups around the arena, and that they intend to demonstrate right after Trump takes the stage. Their goal, he said, is “for Donald to take the stage and to completely interrupt him. The plan is to shut Donald Trump all the way down.”

Trump’s campaign released the following statement:

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. Thank you very much for your attendance and please go in peace.

In a telephone interview after postponing his event in Chicago, Trump said he didn’t “want to see people hurt or worse” at the rally, telling MSNBC, “I think we did the right thing.”

But Chicago police said they had sufficient manpower on scene to handle the situation and did not recommended Trump cancel the rally. That decision was made “independently” by the campaign, said police spokesman Anthony Guglielmi.

Trump said the anger on display in Chicago wasn’t directed at him or his campaign, but rather was a manifestation of the public’s deep frustration with economic conditions in the country.

“Our businesses are being taken away from us, our businesses are being moved out of the country,” Trump said on Fox News. “This is a demonstration against economic conditions on both sides.”

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