Public broadcaster CRTV said witnesses reported that the blaze was raging on the third and fourth floors of the building.
“Firefighters are working to put out the blaze,” it said on Twitter.
“Several deputies from all parties and administrative authorities are helping the deployment of firefighters to stop the flames, which have already ravaged four floors of the administrative block of the building,” it added.
Pictures posted on social media appeared to show a large part of the building had been damaged.
There has so far been no indication of any casualties and the cause of the blaze was not immediately clear.