4 arrested, 2 officers suffer heat exhaustion after protest turns unruly outside Trump rally

Of the four arrested, two face charges of aggravated assault, one faces criminal damage charges and the other was arrested on an unrelated warrant.

The two officers are expected to be OK but were still in the hospital as of late Tuesday night.

Police began deploying pepper balls and tear gas into the crowd, reportedly because people were throwing rocks and bottles at police.

"They had their own gas and they threw it at police. They didn't throw our own gas," Police Chief Jeri Williams said.

She said that's what an employee told her what happened. Williams said it happened near the Herberger Theatre along Monroe Street.

Williams said there was no destruction of property and that it was a "successful celebration."

Phoenix Mayor Greg Stanton highlighted that the rally and the protesters were mostly peaceful except for a few people.

"A very small number of people decided to commit acts of assault on our police officers, including the gas that was mentioned and rocks and that was very unfortunate," Stanton said.

Things escalated just after 8:30 p.m. and then a few minutes of panic followed.

While police said protesters threw gas at them, some protesters told 3TV/CBS 5 that the officers were unprovoked.

Things got so bad that one of our reporters was even forced to don a gas mask after searing smoke began to fill the air in the area of Second Street and Van Buren.

Just after more 9 p.m., and then again around 9:15, more "flash bangs" went too, and more tear gas was sprayed.

Our Mike Watkiss at the scene called it a "battle zone."

"Your eyes are burning; you're choking," said Watkiss, as he described how the gas affected him.

"It was just this thick cloud," described CBS 5 investigative reporter Morgan Loew on the tear gas. "You really have a hard time breathing."

Earlier this evening it looks as if Trump's rally would turn out to be a peaceful event.

But that all changed as the crowds began to spill out of the convention center, and people reportedly started throwing things at police.

An organizer of one of the largest protests said his group did not start the violence.

"It was peaceful," Carlos Garcia of Puente Arizona told our Mike Watkiss. "We started getting shot at by rubber bullets."

When asked if the use of force was justified, Williams said, "Absolutely."

Rep. Ruben Gallego was also at the protest and said he needed to talk to protesters, community leaders and police to figure out what happened.

"It was a great rally on both sides and it was ruined only by a few people," Gallego said.

An investigation is underway and there will be an after-action report.