Firefighters and emergency services were called to the blaze at 2.43am on Monday and found three cars alight.

The fire from those vehicles spread into the depot structure, breaking two glass doors at the entrance to the depot.

MAP: The location where the fire occurred ...

A fourth vehicle was also damaged. All vehicles were owned by council.

NSW Fire and Rescue station officer Tom Fenlon said firefighters spent spent two and a half hours extinguishing the three vehicles and the building.

The fire is being treated as suspicious.

A mixture of 17 administrative and engineering staff work in the building damaged by the fire, and council is currently working to relocate them to other buildings.

While it's too early to tell what was lost, most if not all planning records kept in the building were backed-up electronically off-site.

The council posted an update on their Facebook page confirming police were investigating, while no one was injured in the blaze.

"Staff at the Council Works depot in McLachlan Street are dealing with the impact of a fire that's caused major damage to the depot's main admin building in the early hours of this morning," the post said.

The blaze follows a car burned in the early hours of Saturday morning, while powerpoles were also set alight.