During a news conference held Wednesday night, state officials identified the released hostages as correctional officers.
RAW VIDEO: SWAT team arrives at prison in Smyrna, Del.
Officials said four correctional officers were originally taken hostage, not five as they previously reported.
According to officials, one hostage was released around 2:25 p.m. About three hours later, eight inmates were released. It is not known if the inmates were being held against their will.
Shortly before 8 p.m., Chopper 6 showed a second hostage being wheeled out on a stretcher. Officials say that officer is being treated for unknown injuries.
A group of 19 inmates from Building C could also be seen being taken into police custody at that time.
Officials say negotiations continue for two other correctional officers who are still being held hostage.
RAW VIDEO: Chopper 6 over prison hostage situation in Smyrna, Del.
One correctional officer was injured Wednesday afternoon. We've learned that the 35-year-old guard was struck numerous times with fists and a mop wringer.
That officer was injured, officials said, but those injuries were not life-threatening.
Officials say that officer was not a hostage. He was assigned duties there on Wednesday, but he was located in a different part of the prison because the facility was placed on lockdown.
The incident began in Building C of the complex with a radio call for help around 10:30 a.m. That building houses between 120-150 inmates. It is also where maximum security inmates transition to medium security.
It is not known how many hostage-takers are present, or if they have any demands.
Officials say there is no threat to the public.
All of Delaware's state prisons have been placed on lockdown. That includes the Howard Young Correctional Facility in Wilmington, the Baylor Women's Facility in New Castle, and the Sussex Correctional Institution in Georgetown.
Video from Chopper 6 showed a number of police officers assembling outside the Vaughn facility, along with fire trucks and ambulances.
According to the department's website, the prison is Delaware's largest correctional facility for men, housing about 2,500 inmates. It houses minimum, medium, and maximum security inmates, and also houses Kent County detainees awaiting trial.
It is also the site of the state's death row and where executions were carried out. The prison opened in 1971.
This isn't the first hostage situation at the prison.
In 2004, an inmate raped a counselor and took her hostage for nearly seven hours at the Smyrna prison, according to an Associated Press report at the time. A department sharpshooter later shot and killed 45-year-old Scott Miller, according to the report, ending the standoff.
Stay with ABC13.com as this story develops.