A car has been seized and a man and woman have been arrested after a firearm was found in a rental car near Sydney Airport on Thursday afternoon.

NSW Police were called to a car park close to the Domestic terminal after lunch on Thursday and have confiscated a vehicle that was parked there.

A police investigation is underway at Sydney Airport. Credit:AAP

In a statement on Thursday evening, police said a 23-year-old man and an 18-year-old woman were arrested by Australian Federal Police at the car-rental office at Sydney Domestic Airport at about 2pm.

The man had rented the car on Saturday and returned to the car rental office on Thursday morning to report he had lost the car key, police said.