A fire sent dark smoke billowing from the executive floor of the European Commission headquarters in Brussels Monday, forcing the evacuation of hundreds of workers and visitors.

The cause of the fire was not immediately known, but police said it did not appear to be criminal in origin.

The smoke was seen rising shortly after 1 p.m. from the floor where the European Commissioners have their offices. There was no panic as EU workers filed outside and stood watching the developments. There were no reports of injuries.

Almost a dozen fire trucks quickly moved into the Commission compound, and a helicopter swooped overhead. The smoke disappeared after two hours.

European Commission President Jose Manuel Barroso had to scurry down the stairs to safety from the top floor of the 13-story building. "In a case like this, you don't use elevators," said his spokesman Johannes Laitenberger.

Laitenberger said the firefighters were checking every floor of the iconic star-shaped building, widely seen as the center of EU power. He said it was unclear where the fire had started.

EU Antitrust Commissioner Neelie Kroes made a similar escape from up high. "Me and staff quickly evacuated via the stairs. There was no panic," she said and remained lighthearted. "The rumor is that it came from the kitchen. The potatoes had been cooking too long."

On any given day, some 2,000 bureaucrats, journalists and visitors are in the building.

The Commission building, known as the Berlaymont, was a model of modernism when it was built in 1967 and stood out on its slender pillars for people from miles around.

The four-winged structure was reopened in 2004 after a 13-year renovation and was fitted out with the latest technology, from perfect air-conditioning to fire prevention. It was wrapped in light-grey louvres that move automatically to keep the temperature inside ideal.

Costs of the renovation ballooned to euro670 million, a fivefold increase from the original estimates.

Police spokesman Christian De Coninck said there were no injuries and praised the evacuation operation.

He added that at first sight "there does not seem to be a criminal origin" to the fire.

No damage was visible on the outside of the building.