A correctional officer at a Northern Ontario jail was taken hostage and injured Monday in what the province called a shocking incident.

Details of the disturbance, which took about 12 hours to resolve, emerged Tuesday after the officer and three prisoners were taken to hospital.

The Ministry of Community Safety and Correctional Services said the incident began when inmates took control of a unit in the jail and took a correctional officer hostage.

"This was a shocking incident and a sad reminder that, every day, correctional officers risk their safety to keep our communities safe," said ministry spokesman Greg Flood. "The incident was confined to the jail itself. There were no inmate escapes and there was no threat to the safety of the outside community."

Attorney General Madeleine Meilleur said the officer was released as a result of "successful negotiations."

"Our utmost priority throughout this situation was to bring about a peaceful resolution while ensuring the safety of our staff and the public," she said Tuesday.

Police are conducting a criminal investigation into the incident, while the correctional services ministry is conducting its own internal investigation into what happened.

The officer who was taken hostage was released late Monday night, but the situation at the facility continued until just after 7:30 a.m. Tuesday.

The unit at the centre of the incident was secured with the help of the Corrections Crisis Negotiators and the Institutional Crisis Intervention Teams.

All "non-compliant" inmates have been secured in their cells and a search of the entire facility was underway later on Tuesday morning while the jail remained on lockdown, Flood said. Additional staff have also been brought into the jail from nearby correctional facilities, he said.

The officer who was taken hostage was assessed at hospital and is currently recovering at home, Flood said, without elaborating on the man's injuries.

Of the three prisoners who were also injured, all but one have since returned to custody, Flood added.

The incident also caused physical damage to an area of the jail that included damage to cameras, cell doors and lights, he said.

Throughout the incident, police secured the outside of the jail, while firefighters and paramedics remained on scene.

The incident took place as corrections workers across Ontario are casting ballots in a ratification vote on a tentative contract.