RENOUS, N.B. - Inmates at a federal prison in central New Brunswick were under lockdown Sunday after inmates broke lights, windows, small appliances, sprinklers and tried to start a small fire a night earlier.

Fifty-six inmates in a unit at the maximum-security Atlantic Institute in Renous, about 30 kilometres from Miramichi, refused to return to their cells around 10 p.m. and started throwing chairs and breaking things, said prison spokesman Stephan Breau.

A warden at the prison declared a riot nearly three hours later, and the inmates didn't return to their cells until around 7 a.m. on Sunday.

Breau said staff were able to quickly put out the fire, while the inmates continued to riot. There were no reports of injuries.

Two negotiators from Corrections Canada were called to the prison shortly after midnight to try and convince prisoners to return to their cells.

"If they are causing a disturbance and there's a high risk of damages to property or life then the warden of the institution can decide to read the riot act,'' said Breau.

"When he does, the inmates have an obligation to disperse and cease their actions or they may face criminal charges.''

The unit that was the scene of the riot was still under lockdown on Sunday, while the rest of the prison had returned to normal.

Breau said the riot started because one inmate was not happy with the health services he was receiving. He said he couldn't comment on the inmate's health issues and said he wasn't familiar enough with the case to say whether the care was adequate.

If charges are laid, any sentences given by the court could be added to the inmates' current sentences.

The RCMP did not know if any charges had been laid.

"They will stay on lockdown pending investigation by RCMP and by ourselves. We will only reopen once we've deemed that the safety of staff and inmates is manageable,'' Breau said.

He said maximum-security inmates can be disruptive, and said there have been a number of similar incidents at the prison in the past year.