Angry mobs smashed windows and set small fires in downtown Oakland Thursday night, their rage sparked by a white transit cop’s conviction of a lesser charge in the fatal shooting of an unarmed black man in a subway station New Year’s Day 2009.

The rioting and looting started hours after former police officer Johannes Mehersle was convicted of involuntary manslaughter.

Oscar Grant was shot in the back while laying face-down on a subway platform. Mehersle dodged the more severe charge of second degree murder.

Mehersle faces a prison sentence of two to four years.

The protesters, described by the San Francisco Chronicle as a racially diverse group, faced off with police, threw rocks and bottles, smashed storefronts and sprayed graffiti on walls that read “Riot for Oscar.”

Several trash cans along the streets were set on fire.

“This city is not the wild, wild west,” said Oakland Police Chief Anthony Batts. “This city will not tolerate this sort of activity.”

Earlier in the evening, demonstrations after the verdict had been peaceful as community leaders urged calm.

“I’m angry as hell, but he was found guilty of something,” Tony Coleman, a community organizer who started a movement on Grant’s behalf, said of the convicted ex-cop.

Grant’s family members were outraged at the verdict, with an uncle saying the family had “been slapped in the face” by the justice system.

Grant’s grandfather, meanwhile, told demonstrators to stay calm: “Please don’t tear up the Bay Area,” he said.

During the trial, prosecutors said Mehersle, 28, who was responding to a fight on the subway platform, was angry that Grant, 22, resisted arrest.

The former officer said he accidentally drew his .40-caliber handgun, wanting instead to pull out his Taser.

At least five bystanders filmed the incident.

Eight women and four men sat on the jury, none of whom listed their race as black.

The three-week trial was held in Los Angeles because of riots in Oakland following the shooting.