Rome's Fiumicino airport reopened its main international terminal today after a fire the previous day damaged the building and forced airlines to cancel dozens of flights.

Eighty per cent of check-in desks in the affected Terminal 3 were working normally after hundreds of staff worked through the night to restore service, operator Aeroporti di Roma (AdR) said.

Italy's busiest airport, through which 39 million passengers passed in 2014, was shut down when the blaze started just after midnight (11pm GMT) between Wednesday and yesterday.

At least three suffered from smoke inhalation, but no other injuries were reported.

The fire, believed to have been started by a short circuit in an electrical cabin that was under maintenance in an area of shops, sent thick clouds of smoke billowing out of the building until mid-morning yesterday.

Passengers with flights booked from Terminal 3 were sent to other terminals, where they experienced long delays. Some had to carry their luggage for up to a kilometre because of previous road closures.

Only a shopping area beyond the airport's security controls was damaged by the fire, AdR said in a statement, without specifying how much repairing the damage would cost.

A police source said yesterday there was no indication that the fire was a result of arson, but an investigation was continuing.