The hospital said some of its systems were functioning again Friday morning, but operations haven't yet returned to normal.
Only a limited number of ambulances are being routed to the Jewish and its test centre will remain closed until further notice.
"The hospital is doing its best to minimize inconveniences for its patients and visitors; moreover, there has been absolutely no compromise to patient safety, which is always the top priority of the JGH," the hospital said in a news release issued Friday morning."
The problem is not affecting medical equipment, and no surgeries were cancelled.
"Repairs are ongoing and an update will be sent to the public as soon as it is available."