Ontario's jails are in the midst of a surge of cellblock violence that suggests the province's overcrowded correctional system is simmering with tension, statistics show.

Figures obtained by The Canadian Press under freedom of information reveal there were about 3,000 reported prisoner-on-prisoner assaults in 2012-13 – or eight attacks a day – up almost one-third from the 2,300 attacks five years earlier.

And the number of times guards used physical force against inmates has almost doubled, reaching some 1,500 incidents from 800 in 2008-09.

Penetanguishene’s jail was identified as one of six in the province with more than 200 prisoner-on-prisoner attacks.

The rise in violence comes alongside growing overcrowding in Ontario's jails, with almost half above capacity last year -- another recent high that's seen three inmates locked in cells meant for two.

Glenn Johnson spent eight months in the Elgin-Middlesex Detention Centre in London, Ont., in 2012 while awaiting trial on robbery charges.

After suffering a concussion from a slip in the shower, he said he was "punched out" by inmates demanding his medication -- resulting in a second concussion.

Johnson said he found himself thrown into violence several more times, including when he was stabbed in the back with a pencil, and another time when, he alleges, he was handcuffed and pepper sprayed by guards for laughing.

He said he can't get away from his stint behind bars.

"There's days when I can't even walk out of my house because I suffer from paranoia," said Johnson, who is on medication for the condition.

"And I didn't go in that way. I came out that way."

Johnson is now a representative plaintiff in a proposed class action lawsuit that his lawyer estimates could ultimately include thousands of current and former inmates at the jail.

Correctional Services Ministry spokesman Andrew Morrison said the government is always trying to improve prisoner management.

"Despite our best efforts, violence does occur within a secure correctional facility," Morrison said in an email.

For their part, guards point to overcrowding and a lack of inmate programming as triggers for violence. They also complain about understaffing and poor instruction on handling the estimated one-in-five inmates who have mental health issues.

"We're basically a referee in a hockey game. Except they're not holding sticks, they're holding sharp-edged weapons," said Dan Sidsworth, a guard at the Maplehurst Correctional Complex in Milton, Ont. -- the most violent jail in the province.

According to the statistics, inmate-on-staff incidents, which include uttered threats, jumped to 239 incidents in 2012-13 compared to 169 five years before.

Sidsworth, who is chairman of the corrections division of the Ontario Public Service Employees Union, accused the government of playing down the numbers by recording a single attack against multiple guards as only one incident.

An average of two guards are assaulted daily, he said.

Sidsworth said the government's move to equip staff with handcuffs and pepper foam, along with ending a hiring freeze, should reduce the violence.

After a scathing report last year from the Ontario ombudsman on incidents of excessive use of force and a "code of silence" on reporting them, the Correctional Services Ministry announced a crackdown meant to instill a "cultural shift" in jails.

The ministry promised training, random audits and a "zero-tolerance" policy for threatening or violent behaviour on both sides of the cell bars.

Ministry statistics for the first 10 months of fiscal 2013-14 show about 2,500 inmate-on-inmate attacks, 1,200 use-of-force incidents and about 260 inmate-on-staff incidents.

Six of the province's 29 jails open last year each had more than 200 inmate-on-inmate attacks with facilities in Milton, Lindsay, Hamilton, London, Penetanguishene and Ottawa the most violent.

While the overall number of inmates has dropped in recent years, more prisoners are being held on remand -- awaiting trial or bail. Nearly two-thirds of all inmates now fall into this category.

Jacqueline Tasca, a policy analyst with the John Howard Society of Ontario, said the overcrowding and violence raise deep questions about the justice system.

"The vast majority of people in our system are going to get out," Tasca said. "Do we want prisoners to come out of jail in a better place than when they went in?"

Tasca said a "direct-supervision model" used at two huge new jails in Windsor and Toronto letting guards more easily monitor and interact with prisoners could reduce violence.

Morrison said there are no plans to expand direct supervision to other facilities.