An inmate's knife attack on an officer at Calipatria State Prison on Thursday afternoon escalated into a series of riots that left one prisoner shot dead and at least 16 correctional officers and about 25 inmates wounded, officials said.

A second prisoner who suffered a gunshot wound was airlifted to a San Diego hospital, and five inmates were being treated for severe cuts, bruises and possible internal injuries at Pioneers Memorial Hospital in nearby Brawley.

Also being treated at the hospital in Brawley were two officers, one of whom was the target of the initial attack. The two officers, both of whom suffered head wounds, were expected to be released today.

It was the second riot this month at a state prison. Last week, about 40 inmates were injured at San Quentin in the largest riot at that facility in 23 years.

Order at Calipatria, in the sweltering Imperial Valley, was restored by evening. But the facility, which houses about 3,800 maximum security prisoners and about 300 minimum security inmates, remained under lockdown.

The California Department of Corrections and Rehabilitation said the incident began shortly before 3 p.m., when an inmate at a yard in a maximum-security area stabbed an officer in the head with a handmade knife.

"It escalated from there," said Terry Thornton, a spokeswoman for the department.

The violence spread rapidly as several dozen of the roughly 150 prisoners in the yard attacked correctional officers who had poured in to help their wounded colleague, according to Thornton and Lt. Ray Madden, a spokesman for the prison. Temperatures at the time were above 100 degrees, Madden said.

The initial outburst was quelled quickly, but violence erupted again about 10 minutes later and spread rapidly throughout the yard and into another building, Madden said.

He said there were about four outbursts before order was fully restored, and officers were still herding prisoners back to their cells more than three hours later.

The shots that killed one inmate and severely injured another were fired by officers armed with rifles, but the circumstances surrounding the shootings were not immediately clear, Madden said. Officials said the prisoner who died was shot in the abdomen; the prisoner flown to San Diego was shot in the head. His condition was not made public.

Most of the injuries to officers and inmates apparently resulted from blows from officers' batons and prisoners' makeshift weapons, Madden said.

He said most of the inmates were being treated at the prison infirmary. Except for the two officers who suffered head wounds, all the injured officers were treated and released.

The identities of the officers and prisoners involved in the melees were not released.

"Everything is now under control," Thornton said Thursday evening. "The whole prison is in lockdown."

Ten years ago, eight staff members at the prison were injured when five inmates broke into an office and attacked them with handmade weapons. That attack occurred about two months after an officer shot a prisoner to death during a fight between inmates.

The prison in Calipatria opened in 1992. Although it was designed to accommodate about 2,200 prisoners, there are almost twice as many there now.

The prison is a few miles from the Salton Sea and surrounded by flat, largely treeless farmland. It is about 180 feet below sea level, reputedly at the lowest elevation of any prison in the Western Hemisphere.