55 inmates are taken to hospitals after a riot touched off by fighting among Latino and African American prisoners shuts down a 1,300-man unit of the California Institution for Men.

A dormitory burned down and 55 inmates were taken to hospitals after a riot touched off by fighting among Latino and African American prisoners shut down a 1,300-man unit of the California Institution for Men in Chino on Saturday.

Law enforcement officers gather near the entrance to the California Institution for Men in Chino, where rioting broke out Saturday. All prisons in Southern California were put on lockdown as a result of the disturbance. (Ed Crisostomo / Associated Press)

The riot erupted at 8:20 p.m. in the medium-security dormitory-style barracks of the Reception Center West and lasted until about midnight, according to corrections Lt. Mark Hargrove.

Prisoners ripped pieces of metal from lockers, destroyed beds and broke off pipes to use as weapons. A fire broke out during the chaos, burning down one dormitory. Most of the unit's barracks sustained so much damage as to be uninhabitable.

The disturbance was the prison's most violent since a December 2006 uprising in which 200 inmates rioted for 90 minutes. That racially charged incident was touched off by a fight between a Latino and an African American.

California's prisons, which hold 158,000 inmates, are the most crowded in the nation. Last week, a panel of three federal judges called conditions "appalling" and ruled that the state must shrink its prison population by nearly 43,000 inmates over the next two years to meet constitutional standards.

Following a 2005 Supreme Court decision that found automatic segregation to be illegal, Chino and other California prisons are moving away from the historic practice of separating inmates by race.

Inmates may now share cells with prisoners of different races. The barracks involved in the rioting had been fully integrated.

No guards were reported injured in Saturday's riot, prison officials said.

The fighting erupted in one barracks and quickly spread to six others.

"When you start rioting 200 in a unit, everyone knows it," Hargrove said.

At least 80 officers surrounded the barracks and ordered inmates to come out. Once the riot was quelled, they used pepper spray, batons and foam projectiles to remove inmates who had barricaded themselves inside.

By 7 a.m. Sunday, the barracks were clear. More than 250 inmates suffered injuries, including small cuts, serious stab wounds and head trauma, Hargrove said. By Sunday evening, 17 inmates remained hospitalized.

Some inmates were transferred to other units of the complex, which in all houses 5,911 prisoners.

All prisons in Southern California were put on lockdown as a result of the riot. Visitation was suspended until further notice.

On Sunday, investigators still were determining what caused the melee and what sparked the fire. They planned to inventory the weapons found at the scene.

The California Institution for Men opened in 1941 and serves as a reception center for parolees returning to custody and for newly committed male felons from several Southern California counties.