Workers at the Pirelli office tower were leaving for the day when a small plane smashed into the building, shattering windows, starting a fire and reviving fearful memories of Sept. 11.

Raffaele Taccogna was tending bar at the nearby Atlantic Hotel when he heard the crash Thursday and rushed out, believing it was a terror attack.

"At the beginning, I heard something which seemed like a helicopter. And then I heard something like the engine of the plane which was dying out, and then I heard a terrible explosion," Taccogna said.

"At the beginning I certainly thought of the September attacks in the United States," he said. "It really looked like the same thing."

A reporter who was in front of the nearby central train station said the plane was "in flames" when it hit the building.

"It did not try to deviate its course, but just went straight in," said Fabio Sunik. "Then I saw rubble falling from the building with all the smoking."

Initial reports said at least three people were killed and 60 injured when the plane, en route from Switzerland to Milan's Linate airport, plowed into the Pirelli building, which houses regional government workers.

Debris, including twisted metal and office papers, littered the ground around the landmark building, and streets were closed off in the area, snarling congested rush-hour traffic in the heart of Italy's financial capital.