The Fire and Rescue NSW were called to the intersection of Oxford and Flinders streets, Darlinghurst, about 9.30am today.
They found a bus "well alight" and 30 passengers had got off the bus safely.
The Fire and Rescue NSW spokeswoman said the cause of the fire was not yet known and the investigation was being led by police. There are no injuries.
Fire and Rescue NSW tweeted at 9.54am that the fire had been extinguished.
