PENETANGUISHENE, Ont. -- The head of the union representing employees of an Ontario maximum security jail -- the scene of a riot on Thursday -- says staff shortages are leading to heightened tensions between guards and inmates provincewide.

"I think every institution in Ontario is facing a staffing crisis," said Chris Jackel, president of the union that represents employees at the Central North Correctional Centre in Penetanguishene.

Understaffing could be one of the "hidden contributing factors" to the rising tensions, said Jackel, who was also a member of a tactical team that responded to the riot by 45 inmates in two separate wings of the facility.

"Our institution does see very frequent lockdowns generally due to lack of staff."

Inmates damaged doors, ripped phones off walls, tried to breach a door that connected two wings, covered floors with soap, shampoo and garbage and used socks filled with "heavy material" as weapons before guards used pepper spray to subdue them, Jackel said.

"(They) were actively causing damage to the two wings, just trying to break as much as they could," he said, adding the riot took six hours to get completely under control.

Tammy Carson, the union's provincial health and safety chair, said that lower staff numbers have also prevented guards from conducting proper searches of cells, leading prisoners to stockpile items like shampoo and pepper for use in riots against guards.

"We're so short-staffed right now and with summer coming ... unfortunately I really don't anticipate it getting better before it gets worse," she said, adding the Penetanguishene prison currently holds between 800 to 900 inmates with a total capacity of 1,150.

"I think this is going to become the norm ... institutions are going to be locking down (for) major parts of the summer because we have no staff."

A 2013 report by Ontario ombudsman Andre Marin on violence against inmates by guards highlighted the "code of silence" among guards in the province, and found that overcrowding and understaffing in provincial jails exacerbated tensions between inmates and staff.

The union responded to the report at the time by saying that the problem of "chronic understaffing" was one of the root causes of violence behind bars.

Greg Flood, a spokesman for Ontario's ministry of Community Safety and Correctional Services, said in an emailed statement that the disturbance came to a peaceful resolution and no injuries were reported. He said that an internal investigation is ongoing while "minor repairs" were being made to the cells.

-- By Adam Miller, Toronto