CALIFORNIA ? A female correctional officer was released unharmed Saturday evening after a 10-hour hostage standoff that prompted a lockdown at a state prison, authorities said.

Michael David Watson, 41, released the hostage, Sheila Mitchell, 45, without incident after 5 p.m., according to California State Prison, Sacramento spokeswoman Lt. Joyce McClendon.

The standoff began about 7 a.m. when Watson, armed with a six-inch metal knife made in the prison, grabbed Mitchell in the prison dining room and pulled her into an office, officials said. It was unclear how many inmates were in the dining room at the time.

The prison was secured and placed on full lockdown as officials negotiated over the phone with Watson, a maximum-security inmate who had been assigned to work in the dining room.

Neither Watson nor Mitchell were injured.