OAKLAND, Calif. -- 120 demonstrators were arrested overnight as a march to protest the slaying of a Hayward man by a BART police officer erupted into violence in downtown Oakland.

Authorities said 120 people had been arrested in the protest over the fatal New Years Day shooting of Oscar Grant III after a splitter group broke off from the peaceful march and began trashing store fronts, breaking windows, setting fires and damaging at least one patrol car and several other vehicles. Most were cited and released.

“We live a life of fear and we want them to feel fear tonight,” an unnamed demonstrator told KTVU at the height of the violence.

Oakland Mayor Ron Dellums, who had walked to City Hall alongside dozens of protest at the start of the march, called for calm as the demonstration reeled out of control.

"Even with our anger and our pain, let's still address each other with a degree of civility and calmness and not make this tragedy an excuse to engage in violence," Dellums said. "I don't want anybody hurt, I don't want anybody killed."

However, many of the demonstrators booed the mayor and decried the incident as yet another case of police brutality. Rodesha Morgan, 22, who said she is the niece of Mack Woodfox, a man fatally shot by an Oakland police officer last year, was one of the demonstrators walking alongside Dellums.

"I'm out here because my uncle was killed," Morgan said. "I live with it every day."

She shouted toward Dellums, "How many people have to die before something gets done?" Several people gathered at the Fruitvale Bay Area Rapid Transit station Wednesday afternoon for a rally to protest the shooting death of Grant at the hands of a transit agency police officer at the station early Jan. 1.

For safety reasons, BART trains bypassed the Fruitvale station while the protest continued. Organizers said the rally was planned to last until 8 p.m., but by 5:30 most of those gathered spontaneously started marching through the streets of Oakland towards downtown.

While the majority of the marchers were well behaved, just after 6:30 p.m. a splinter group of protesters started causing trouble at the intersection of 8th Street and Madison not far from the Lake Merritt BART station.

A fire was lit in a dumpster on wheels that was rolled into the middle of the street and swarmed a police car that was nearly tipped over as the angry protestors beat on the vehicle with sticks and rocked it violently back and forth.

Oakland police responded in riot gear, shooting tear gas and approaching the crowd with shields, helmets and batons drawn to force them to disperse. The Oakland Fire Department was quickly able to put out the dumpster fire without event.

Authorities shut down the Lake Merritt BART station for a time during the altercation before the crowd surged toward downtown.

The demonstrators reached the intersection of Broadway and 14th Street, half a block from Oakland City Hall.

A line of police officers kept the crowd from moving toward the civic center. For a time there was a standoff as some demonstrators lay in the street to show their solidarity with the slain BART victim.

Police on loudspeakers told the crowd there would be arrests of people didn't leave. Moments later, another small street fire erupted and police made their move to push the crowd back.

"The crowd started to become more agitated, more hostile, started throwing stuff at the police," Oakland police spokesman Jeff Thomason said. "We gave a dispersal order four to five times over a 20-minute period, then we had our officers go in and start making arrests."

The crowd surged down 14th Street, setting fires in garbage cans and smashing car and store windows along the way.

More than 100 officers faced off with the protestors for about an hour at Broadway and 14th. The group was mostly young people who shouted epithets.

Some of them laid face down on the ground in front of the officers, imitating the position that Grant was in when a BART officer shot him to death last week.

City Councilman Ignacio De la Fuente rushed through the crowd on his way into City Hall.

"It's an incredible tragedy that happened, and obviously that's the reason why we are meeting," explained De la Fuente. "We are meeting so we can see what we can do to make that the people know that we are going to do a fair investigation. Then justice will be done."

As the protesters splintered into smaller groups with police in pursuit, at least three parked vehicles were set on fire, forcing more Fire Department response in the already congested and chaotic area.

BART officials announced early Thursday that they were beefing up security at all stations and a transit board meeting was scheduled for Thursday morning.