ROME - An electrical short circuit is being investigated as the probable cause of a fire that badly damaged part of Rome's Fiumicino airport and closed it to most traffic Thursday morning, the head of Italy's civil aviation authority said.

ENAC president Vito Riggio told a news conference that investigators are still investigating the cause of the fire inside the international terminal of Italy's busiest airport, but that it appeared to have been a short-circuit in a restaurant.

Three people suffered light smoke inhalation, authorities said. Foul play was not suspected in the blaze.

Some 450 square metres of retail space was involved in the fire, which broke out just after midnight and was brought under control about five hours later, Riggio said.

Damage was contained to the commercial area located beyond the security check-in, said the head of Rome's airport, Lorenzo Lo Presti.

Nineteen international long-range flights were permitted to land Thursday morning, but all other traffic was blocked, with passengers being transported to the centre of Rome by special trains. Departures were resuming after noon at a rate of 12 an hour and normal service was expected by 2 p.m.

Fiumicino is Italy's busiest airport, with some 130,000 passengers a day. The international terminal was not accessible, and flights were being reassigned to other terminals.

Images broadcast on Sky TG24 showed part of the international terminal engulfed in flames overnight, and by morning the burnt-out facade of part of the terminal was evident from outside. Smoke was still coming from the building hours after the flames were doused.