An investigation was underway Thursday to determine the cause of a fire that caused major damage to a storage facility on the north end of Riverside.

The non-injury blaze was reported just after 1 a.m. Wednesday at Cube Smart Storage in the 4000 block of Fairgrounds Street, near the Pomona (60) Freeway, according to the Riverside Fire Department.

Battalion Chief Bruce Vanderhorst said that three engine crews and a truck company, numbering 17 personnel, were sent to the location and encountered "four storage units ... actively burning."

Vanderhorst said firefighters initiated a suppression effort that fully contained the blaze within a half-hour.

"The cause of the fire could not be determined at the time," the battalion chief said. "There were no signs of forced entry into the affected storage units, nor were any incendiary devices found."

Fire prevention officers were summoned to conduct a more thorough investigation, which was continuing Thursday.

Vanderhorst said the goal was to pull security surveillance video camera tape "for further insights" as to what may have transpired at the location.