Washington, Feb 2 (IANS): A 12-hour long US prison standoff continues in Delaware with four out of five employees still remaining hostage with the inmates, a media report said on Thursday.

The single hostage released was sent to a hospital, a police spokesperson said, Xinhua news agency reported.

The FBI and Delaware state police continued negotiations with inmates inside a building of the Level 5 James T. Vaughn Correctional Center (JVTCC) in Smyrna, some 149 km from here, said Sergent Richard Bratz, the state police spokesman.

The incident began around 10.30 a.m. on Wednesday when a guard radioed for immediate assistance from inside the building housing more than 100 inmates, said Bratz.

He did not reveal whether the authorities had received any demands from prisoners.

"We are doing everything we can to ensure the safety of everyone involved and using all of our available resources," Bratz said.

Citing the officers association, CNN said four guards and one counsellor were taken hostage by inmates, while one guard was released.

"It's a very scary situation right now," Geoff Klopp, president of the Correctional Officers Association of Delaware said.

A large number of local emergency responders, including policemen from Delaware and neighbouring Pennsylvania, were seen rushing to the prison around midday.

All Level 5 Delaware prisons, the state's maximum security facilities, were placed on lockdown in the day as a result, though a corrections department spokeswoman said it was an isolated incident.

Opened in 1971, the JVTCC has been Delaware's largest correctional facility for men, housing about 2,500 minimum, medium and maximum security prisoners as well as the state's death row inmates.

It also housed facilities for executions, said the State Bureau of Prisons.