OAKLAND -- Police declared unlawful assembly and were trying to disperse a crowd near Broadway and 14th Street after violence broke out Sunday night in the aftermath of the George Zimmerman acquittal in the shooting death of Trayvon Martin.

A largely peaceful crowed of protesters marched through downtown Oakland on Sunday afternoon, but when nightfall struck, a small crowd began breaking windows and spray painting graffiti along Broadway.

At least two journalists, including a Bay Area News Group photographer and a TV cameraman were attacked -- one knocked over into bushes and the other thrown to the ground, swarmed and kicked by at least half a dozen assailants wearing black ski masks.

Neither sustained serious injury but their equipment was damaged in the fracas.

In the late-afternoon march, which started at Frank Ogawa Plaza in downtown Oakland, hundreds of protesters traversed some four-to-five miles and circled back to 14th Street and Broadway where they sat down about 7 p.m., blocking the intersection.

Marchers had been on the move for more than two hours, with police monitoring the crowd.

As of 11 p.m. no arrests had been made. But about 10 p.m., a smaller group of protesters began vandalizing businesses along Broadway and Telegraph.

During the afternoon demonstration, there were chants and shouts. "Rest in peace Trayvon Martin; Rest in peace Alan Blueford; Rest in peace Oscar Grant. End the violence," shouted Sellassi Blackwell, 30, of San Francisco, as a crowd before him cheered.

"We are all Trayvon," said Reiko Redmonde, who organized Bay Area protests. "This is not just a question for black youth but for all peoples' humanity, a question of what kind of society and what kind of world we want to live in."

Downtown property owners cleaned up storefronts damaged in a chaotic Saturday night protest as the demonstrations were held Sunday afternoon in Oakland and San Francisco.

Protests had been planned Sunday in East Oakland at 73rd Avenue and International Boulevard, and also at 14th Street and Broadway, and Powell and Market streets in San Francisco. They were part of protests nationwide, with rallies Sunday in Florida, Philadelphia, New York, Chicago, Fresno, Cleveland, and Los Angeles, where a demonstration turned violent.

There, people walked onto Interstate 10 by the Crenshaw Avenue exit and clashed with police. At a nearby street corner a crowd threw rocks and batteries at officers, who fired beanbag rounds. There were no arrests.

The Bay Area demonstrations came after a march that began Saturday, hours after a jury acquitted Zimmerman in a Florida courtroom. At 12:30 a.m. Sunday, Oakland protesters knocked trash cans into the street and sometimes set the contents alight, creating small fires amid cheers from onlookers.

One man was being beaten by multiple attackers in a Broadway doorway near Frank Ogawa Plaza until other protesters surrounded the skirmish and yelled at the combatants to stop. The man was helped to his feet and did not appear to be seriously injured.

Around 12:45 a.m., demonstrators remained in the area around 19th and Telegraph but numbers had significantly diminished. Some shouted that police were trying to "kettle" them, or corral them into a limited area.

On Sunday morning, property owners were boarding up storefronts and cleaning graffiti, but broken glass remained on sidewalks along Telegraph Avenue and Broadway, the two thoroughfares that bore the brunt of the vandalism.

Among the businesses damaged were Sears, the Oakland Tribune, and Flora, a restaurant in the 1900 block of Telegraph Avenue that was nevertheless busy during the lunch hour Sunday.

In a statement, Oakland Mayor Jean Quan said, "a small group of people gathered in downtown Oakland last night. Sadly, some of them dishonored the memory of Trayvon by engaging in violent activities that hurt our growing economy and endangered people.

"This is unacceptable as well. We will not tolerate violence in our city. We must come together to heal and move forward," Quan said. "In the days and weeks ahead our community will continue working to learn from this tragedy and to prevent this from ever happening again."

Eric Kurhi contributed to this report. Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund. David DeBolt covers breaking news. Contact him at ddebolt@bayareanewsgroup.com. Follow him at Twitter.com/daviddebolt. AP contributed to this story.