Punches were later thrown between supporters of the Republican presidential front runner and protesters
Republican presidential candidate Donald Trump has cancelled a rally in Chicago due to security concerns.
Violence broke out at the University of Illinois after an announcement was made that the rally would be postponed.
Supporters of Mr Trump shouted "We want Trump! We want Trump!" while protesters who packed into the university's arena cheered.
Punches were later thrown between supporters of the Republican presidential front runner and protesters.
University staff had petitioned administrators to cancel the rally, citing concerns about a "hostile and physically dangerous environment".
A statement from Mr Trump's campaign said he met with law enforcement officials after arriving in Chicago.
The statement added: "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."
Hundreds of people gathered outside the arena in the hours before the event was scheduled to begin.
Supporters of Mr Trump were separated from an equally large crowd of protesters by a heavy police presence and barricades.
Earlier in the day Mr Trump was interrupted by protesters several times at a rally in St Louis, Missouri.
It comes as the former Republican candidate Ben Carson endorsed Mr Trump ahead of what could be the decisive week in the party's nomination race.
The retired neurosurgeon joined Mr Trump in a news conference on Friday morning at the real estate tycoon's Mar-a-Lago club in Palm Beach, Florida.
Mr Carson said: "I've come to know Donald Trump over the last few years. He is actually a very intelligent man who cares deeply about America."