The blaze started on the third floor of the I-T office located in multi-storeyed Scindia House and efforts are on to douse it, he said.
"Our control room received information at 4.55 pm about a fire erupting on the third floor of the ground plus six-storeyed building.
"Five fire engines, four water tankers along with adequate number of fire brigade personnel were rushed to the site to douse the flames," the official said.
No injuries were reported so far, but one person trapped on the second floor of the commercial building was rescued by firefighters, he said.
The building, a well-known landmark in South Mumbai, also houses the office of the Debt Recovery Tribunal (DRT).
Witnesses posted images and videos of the fire on social media.