Updated

What started as a peaceful immigrants' rights march in California turned violent on Saturday, culminating in damage to nearly 20 businesses, at least one arrest and "anarchist graffiti" left on several buildings.

Santa Cruz Police spokesman Zach Friend said roughly 250 people marched through the city at around 10:30 p.m. Saturday. The "unpermitted and unsanctioned event" was running smoothly until some individuals in the crowd began breaking windows and spraying graffiti on retail shops in the city's downtown corridor.

It was unclear if the damage was caused by people marching in support of immigrants' rights or if the group was "infiltrated by anarchists," Friend said in reference to anarchy signs that were spray-painted on some of the buildings.

"They're a group of people who seem to fancy themselves as revolutionaries, but what they really are are a group of morons," said Friend, adding that a fire in a coffee shop had been extinguished.

A total of 18 businesses were damaged, with cost of repairs estimated at between $50,000 and $100,000. Police were able to restore order once officers arrived from other agencies, Friend said.

One person was arrested on suspicion of committing vandalism, the Associated Press reported, although other local reports indicated at least two people had been arrested.

Friend said police expect to make additional arrests once detectives gather video of the event.

"I assure you, more people will be held accountable for this as we review videos," Friend said.

Santa Cruz Police Capt. Steve Clark told the San Jose Mercury News that many of the protesters carried makeshift torches and wrote "anarchist graffiti" on buildings.

Clark continued, "The damage that was caused was without purpose. It was senseless violence that victimized a community who cannot afford to be victimized in this manner. This did nothing to add credit to whatever they believed their cause was."

Syndicated columnist and Fox News contributor Michelle Malkin said the arrests and rioting were not reported by many mainstream media outlets. She said many videos of the tumultuous march can be seen on YouTube.

"Now can you imagine if there were 250 tea party activists carrying torches and throwing rocks through businesses?" Malkin told Fox News on Monday. "We'd be hearing about it everywhere. But these are the May Day melees that you aren't going to see anywhere else."

Elsewhere, in San Francisco, where demonstrations were also held in protest of Arizona's tough new immigration law, three people who were part of a demonstration held by the Minutemen -- a group in favor of Arizona's new law -- were attacked and at least two were arrested, KGO reported.

The Associated Press contributed to this report.