"We are investigating this as a matter of urgency and will provide an update shortly", it said.
A spokesman for the airport, which handles more than 20 million passengers a year, said: 'Due to a fire on the auto park shuttle bus, terminal forecourt and surrounded area including parts of the terminal building are being evacuated due to smoke.
The terminal forecourt and parts of the terminal building were cleared of people after a blaze broke out at about 4pm today (Friday).
The fire is understood to have engulfed a bus which was parked outside the terminal building.
He added the fire was extinguish by 5.02pm although fire crews remain on the scene, using thermal imaging cameras to make sure there are no remaining hotspots.
"Due to the earlier evacuation of the terminal, all passengers are now in the process of being re-screened through security".
"We advise all passengers due to depart this evening to contact their airline directly for the up-to-date flight information".