PORTLAND, Ore. - Crowds swelled to several thousand as demonstrators from varying groups converged Sunday afternoon in downtown Portland, Oregon, in the wake of the fatal stabbing of two men who tried to stop another man's anti-Muslim tirade.

At about 3:30 p.m., police announced the south side of Chapman Square, which had been designated for an Antifa group to gather, had been closed. Officers started to employ "impact weapons and chemical munitions" after protesters began throwing objects. Shortly after, police said all of Chapman Square had been closed.

Protesters threw bricks, mortars and balloons filled with "unknown, foul-smelling liquid," according to police. They said only the protesters at Chapman Square engaged in criminal behavior. The crowds at Terry Schrunk Plaza, where the Free Speech Rally was held, and City Hall, where the Portland Stands United Against Hate Rally took place, were not involved.

Police pushed the crowd of protesters from Chapman Square to Lownsdale Square, where they continued to throw objects at officers. Police said the "suspects [would] be arrested if/when possible."

A pro-Donald Trump free speech rally organized by a conservative group has started. Kyle Chapman, the speaker for the planned event, told media earlier Sunday that it's good to see people "uniting under the banner of American nationalism."

Meanwhile, a number of community groups organized counter demonstrations to rally against hate and racism.

Hundreds of people on the steps of City Hall are holding signs that read "Our city is greater than hate" and "Black lives matter." They're chanting "love, not hate."

Other demonstrators across the street are chanting "USA" and holding banners in support of President Donald Trump.

Dozens of police officers in black protective gear and others on bicycles are in downtown Portland working to keep various groups separated. They have also used yellow tape to keep the groups away from each other.

"Protesters should stay with their groups, not attempt to cross streets to escalate tensions," Portland police said in a tweet.

Portland police report that three people have been arrested and officers have confiscated several weapons.

PHOTOS: Weapons confiscated at downtown Portland demonstrations

PHOTOS: Protests, counter-protests in downtown Portland

At least five different rallies or protests are planned in different parts of Portland on Sunday, with four of them scheduled for downtown.

Police said before the protests began that they had planned a "robust law enforcement presence due to online threats of violence between different groups." They warned people not to bring any weapons or items that can be used as weapons to any of the events.

KGW will have live-streaming coverage throughout Sunday's rallies. Watch live-stream coverage here. App users: Click here to watch live.

The following agencies will be helping the Portland Police Bureau ensure public safety on Sunday:

  • Oregon State Police
  • Multnomah County Sheriff's Office
  • Federal Protective Service
  • Department of Homeland Security
  • Federal Bureau of Investigation
  • United States Attorney's Office
  • Multnomah County District Attorney's Office
  • Portland Fire & Rescue

The Associated Press contributed to this report.