Were you told by the crew it was a fire? Or could it have been a compressor stall? Fires are very rare, compressor stalls are less rare.

From http://en.wikipedia.org/wiki/Compressor_stall:

Compressor stalls, or compressor surges, are immediately identifiable because they produce one or more extremely loud bangs from the engine. Reports of fire or flames "shooting" out of the engine are common during this type of compressor stall. These stalls may be accompanied by an increased exhaust gas temperature, an increase in rotor speed due to the large reduction in work done by the stalled compressor and yawing of the aircraft in the direction of the affected engine due to the loss of thrust. Severe stresses occur within the engine and aircraft particularly from the intense aerodynamic buffeting within the compressor.