No serious injuries were reported as a result of a blaze which took hold around 5:00 am (0300 GMT) in terminal three of the Italian capital's main hub, which is located on the coast around 30km (20 miles) west of the city.
Several airport employees were suffering from the effects of smoke inhalation, airport officials said.
Around 50 firemen took two hours to get the fire under control and the building was still smouldering at 9:30 am (0730 GMT).
Firemen inspect Rome's Fiumicino airport main international terminal after a fire broke out overnight, Thursday, May 7, 2015. - Massimo Percossi/ANSA via AP
Access to the airport was blocked with authorities saying it would not reopen to passengers until 2:00 pm (1200 GMT).Shorthaul flights to and from Rome were cancelled but intercontinental planes arriving after overnight flights were able to land.
There was no immediate indication of the cause of the fire.
Italian media reported that around four hundred square metres of shops in the terminal had been severely damaged by the blaze.
Alitalia, the airline which has the most flights to and from the airport, warned that the disruption could lead to delays and cancellations throughout the day and advised passengers they could switch to alternative flights up until May 10 or have the price of their tickets reimbursed.