County jails were on lockdown status Thursday following a series of brawls that left at least 19 inmates injured at a facility that was hit last week with deadly rioting, authorities said.

A brawl involving about 300 inmates broke out about 8:30 p.m. Wednesday at the medium security North Facility of Pitchess Detention Center in Castaic, about 40 miles northwest of downtown Los Angeles, said sheriff's Sgt. Don Manumaleuna.

"Deputies were able to regain control of the facility, and at this time they're investigating the cause of the disturbance," he said.

The fight followed four racially motivated fights involving more than 450 black and Hispanic inmates that broke out in the afternoon at the center's east facility. A total of 19 inmates were injured in the brawls, one critically, said sheriff's Deputy Bill Spear.

Four inmates were transported to hospitals. One had a head injury and the others sustained superficial cuts. Fifteen more were treated at the facility for minor injuries. No sheriff's deputies were hurt.

The fighting began after more than 120 inmates housed inside a group dorm separated themselves along racial lines. The violence was quickly put down, but similar fights occurred in little more than an hour at three more dorms, leading deputies to fire sting balls on inmates to gain control, said sheriff's Sgt. Diane Hecht.

All seven county jails were subsequently placed on lockdown, according to sheriff's officials. The lockdown was expected to last through Thursday, Spear said.

Another section of the same detention center was the site of rioting Saturday between Hispanic and black inmates that killed one man and injured more than 100 others. It was followed by two other melees Monday night that caused one minor injury.

Investigators were looking into the cause and timing of Wednesday's fights as well as possible links to recent outbreaks of violence at the center.

In those, authorities suspect gang leaders outside the jail contacted Hispanic associates inside and directed them to attack blacks as retaliation for a recent assault in South Los Angeles.

In an interview with The Associated Press, California Corrections Secretary Roderick Q. Hickman said that his department has offered to work with sheriff's officials — whose jails often feed into the state prison system — as they investigate the weekend violence.

He said state authorities want to know what's causing the county's problems so they don't spill over into the statewide prison system.

In Central California, four inmates were hurt in fighting that began Tuesday at the California Correctional Training Facility in Soledad. That uprising prompted authorities to place a prison unit on lockdown Wednesday.

The fracas, which involved hundreds of black, Latino and white inmates, was not believed to be connected to the violence in the Los Angeles County jail, corrections spokesman J.P. Tremblay said.