Around 1,200 people gathered for the protests on Saturday, which forced authorities to close several bridges and roads in the city, Efe news quoted Portland Police Chief Danielle Outlaw as saying in a press conference.
"Officers made at least 13 arrests," Outlaw said, adding that six protesters suffered minor injuries, not caused by officers.
The police also reported the seizure of weapons including metal and wooden poles, knives, shields, chemical spray and a stun gun.
Outlaw said those arrested face a range of charges, including disorderly conduct, interfering with police, resisting arrest, possessing a weapon and unlawful use of a weapon.
The demonstrators began assembling at 8.30 a.m. on Saturday morning in the central area of the city and at around 4.15 p.m., a "civil disturbance" situation was declared after reports of numerous conflicts between the protesters.
Portland, considered one of the most progressive cities in the US and which was the scene in 2016 of some of the most massive protests against the election of President Donald Trump, witnessed similar demonstrations last August that were calm from the start to finish.
This year, right-wing leaders called an "End Domestic Terrorism" protest against Antifa, a leftist anti-fascist group.
The rally was attended by the far-right groups Proud Boys, which civil rights organization Southern Poverty Law Center defines as a hate movement, and Patriot Prayer.
In response to the protests, Antifa also took to the streets in counter-demonstrations.
During the press conference on Friday, Portland Mayor Ted Wheeler said that the police and supporting authorities "were tasked with an extremely difficult job, and performed like the true professionals that they are."
"We were preparing for the worst case scenario. We are relieved that this did not happen," he added.
Trump weighed in on his Twitter account during the day, saying that "Portland is being watched very closely."
"Hopefully the Mayor will be able to properly do his job!" Trump said, adding that "major consideration is being given to naming ANTIFA an "ORGANIZATION OF TERROR."
The authorities were on alert to prevent the protests from resulting in violent acts such as that in Aug. 2017, when a neo-Nazi rammed his vehicle through a crowd during protests in Charlottesville, Virginia, leaving one dead and scores injured.
( With inputs from IANS )