ROME (TIP): Rome’s main Fiumicino airport was gradually reopening on Thursday after a fire badly damaged the main international terminal building and forced the cancellation of dozens of flights, leaving hundreds of passengers stranded.

The airport, Italy’s busiest with 39 million passengers in 2014, was shut down when the blaze started in Terminal 3 just after midnight (2200 GMT).

As services slowly resumed, travellers, some of whom had to carry their luggage for up to a kilometre because of previous road closures, were being sent to other terminals, where they experienced long delays.

The fire, which one official called “very violent”, sent thick clouds of smoke billowing out of the building until mid-morning. It was believed to have been started by a short circuit in an electrical cabin that was under maintenance in an area of shops, an airport official told reporters.

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

At least three people suffered smoke inhalation, a fire brigade official said, adding that the situation might have been much worse had the fire broken out during the day, when the terminal is crowded. A number of shops were seriously damaged.”We got here and there was just a cloud of smoke and a terrible smell, the air was so bad we couldn’t breathe. There weren’t any masks or anything,” said passenger Andrea Lauretti.

Alitalia, Italy’s national carrier which earlier had cancelled all flights to and from Fiumicino except some inter-continental arrivals, said check-in procedures would be moved to Terminal 1 until further notice.

Passengers who had arrived for early morning flights were not allowed inside any of the terminals. The main highway linking the airport to Rome was closed during the night and the train service from the city centre was suspended.

The airport is almost wholly owned by Italian infrastructure company Atlantia. Sources said this week that Atlantia had received expressions of interest to buy a 15 percent stake in its airport unit Aeroporti di Roma (AdR), which runs Rome’s two main airports.