The city’s jail system is in “deep trouble” according to an assessment by the new Corrections Commissioner.

Testifying before a City Council budget hearing Monday, jails chief Joe Ponte said the department’s performance under his predecessor, Dora Shiro, was “unacceptable.”

It was one of the sharpest attacks on the Bloomberg administration made by a de Blasio appointee.

Ponte headed up Maine’s correction agency before being appointed by de Blasio in March.

Ponte said that over the past four years, use of force is up 59 percent, slashings and stabbings have doubled, and assaults on staff are up 30 percent. Overtime costs jumped from $97 million to $155 million.

“Figuring out what happened . . . and then developing something to improve that will take a little bit of time,” he said.