No injuries or casualties have been reported so far, they said.
The blaze started on the 21st floor of Lotus Business Park on Andheri Link road, and later spread to the 20th floor, according to fire brigade officials.
"We got a call at around 11 AM that a fire has broken out in the commercial building. We initially thought it was a grade-1 fire and sent four fire tankers to the spot. The fire was then upgraded to grade 2 and we have now deployed 12 fire engines and nine water tankers at the site," a fire brigade official told PTI.
"There was lot of smoke emanating from the top floors where the fire broke out. This caused panic among the people working there, which made the evacuation process a little difficult. But as per initial reports, the fire brigade has managed to evacuate everyone," a municipal official said.