Last Updated Mar 12, 2016 9:43 AM EST
Anger surrounding Donald Trump's presidential campaign reached a boiling point in Chicago Friday night.
The Republican front-runner canceled a campaign rally over security concerns when thousands of protesters gathered outside an arena at the University of Illinois, then flooded the venue where he was scheduled to speak, reports CBS News correspondent Dean Reynolds.
Trump's campaign events have turned increasingly hostile with sometimes violent confrontations between his supporters and demonstrators.
Five people were arrested, but the demonstrators were mostly peaceful, and police say they did not recommend Trump cancel the event.
The announcement by a Trump staffer postponing the event set off celebrations for some and disappointment for others.
As police tried to clear the pavilion, some fights broke out. Demonstrators - many of whom are students at the University of Illinois Chicago - say Trump received their message.
Trump loyalists say the protest is an attack on free speech.
"They are the intolerant ones. They can't stand if somebody has an opinion that's not theirs," one said.
As the heated exchanges continued outside the arena, Trump explained why he canceled the event.
"I don't want to see any of the people hurt either inside or outside. And the law enforcement said they just don't have enough men to cover," Trump said.
But Chicago police say that's not the case.
"I can tell you that we did assure the Trump campaign that we had more than adequate resources," said acting Chicago Police Supt. John Escalante.
One officer was hurt outside when he was struck with a bottle.
Tensions at Trump rallies have been stewing for some time. Earlier on Friday, three dozen people were arrested at an event in St. Louis.
And this week, a protester being led out of a North Carolina rally appeared to be sucker-punched by a Trump supporter.
Trump's chief Republican rival, Ted Cruz, called it a sad day, and laid some of the responsibility at the feet of the GOP front-runner, accusing his campaign of "affirmatively" encouraging violence and "this sort of nasty discourse."
Some of the demonstrators were heard chanting Bernie Sanders' name during the rally.
Trump had canceled an event scheduled for Sunday in Cincinnati, but on Saturday morning he tweeted that it was "on." He has another in Kansas City, Missouri, on Saturday. Mayor Sly James is advising people to avoid conflict, and says if you're concerned, do not attend.