AP
Thursday: Smoke billows from the Pirelli building after a small plane crashed into it.

MILAN, Italy — A small plane smashed into the tallest building in Milan Thursday evening, causing smoke to pour out of the heavily damaged top floors of the skyscraper. At least five people were reported killed and 60 others were injured.

There were initial fears that the midtown crash was a terrorist attack — it was the second time since Sept. 11 that a plane has struck a high-rise building — but officials later said that it appeared to have been a tragic accident.

"It sounded like a bomb. The pavement shook like an earthquake," said a woman identifying herself only as Lucia.

In Washington, a senior Bush administration official, speaking on condition of anonymity, said Italian officials had told the United States that a mechanical problem not related to terrorism caused the crash. The pilot had sent out a distress call, saying he had landing gear problems.

Some eyewitnesses reported that the plane was on fire before crashing into the 30-story Pirelli building, Milan Police Office Celerissimo De Simone said.

The Rockwell Commander plane, en route from Switzerland on a 20-minute flight to Milan, punched a hole in the 25th floor of the building, sparking a smoky fire that was quickly put out. Rescuers helped bloodied men in business suits evacuate the building.

The weather was clear at the time of the crash, which occurred near the end of the work day and left gaping holes on both sides of the slim skyscraper. A large section of an entire floor lost its walls, and smoke and liquid poured from the gash in one side of the building.

"The initial information that the Interior Ministry has leads us to lean toward an accident," Interior Minister Claudio Scajola said.

The pilot, identified as 75-year-old Luigi Sasulo of Pregassona, Switzerland, had sent out a distress call at 5:54 p.m. just before the crash near Milan's main train station, said De Simone.

RAI state TV reported that the pilot said he was experiencing engine trouble.

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"We believe it isn't a terrorist attack," said police Sgt. Vincenzo Curto, who was reached at the Carabinieri headquarters in Milan. "The pilot might have taken ill or it was an engine problem."

In Rome, a spokesman for the senate president, Marcello Pera, said the interior minister had informed him that the crash didn't appear to be a terror attack. Earlier, Pera had said it "very probably" was an attack.

The plane had taken off from Locarno, Switzerland, 50 miles northwest of Milan, and was heading to Milan's Linate airport.

Patrick Herr, spokesman for the Swiss air traffic control office SKYGUIDE, said the plane left Locarno at 5.15 p.m.

A woman who worked on the eighth floor, well below the crash, said she saw 10 people injured and bleeding. News reports said at least 30 were taken to the hospital.

One Milan hospital, Fatebene Fratelli, said it had received 20 injured, including a woman with burns.

"It was shocking," said Luccheta Antonio, 52, a barber down the block. "The windows shook, and the mirrors."

"It was a violent explosion," said Stefano Bottazzi, 35, who works in a skyscraper 500 yards from building. "The clock fell to the floor."

On the streets, rescue workers in orange uniforms helped the injured. Ambulances streamed into the area and pedestrians peered upward.

As ambulance crews worked, a man with his shirt splattered with blood and his hand covering a gash on his head was rushed from the scene. Police cordoned off the area as passersby gawked at the skyscraper.

At 30 stories high, the Pirelli structure, located near the central train station, is Italy's first skyscraper and one of the world's tallest concrete buildings. It was built in 1958 and designed by architects Gio Ponti and Pier Luigi Nervi. The building is one of the main symbols of Milan, along with the city's cathedral.

The skyscraper, built of concrete and glass with a diamond-shaped floor plan, has inspired design around the world including the MetLife building in New York.

National Security Adviser Condoleezza Rice and White House chief of staff Andrew Card broke the news of the crash to President Bush, White House press secretary Ari Fleischer said.

"I think you can presume that we will be — if we are not already — in touch with Italian authorities and will ascertain precisely what the facts are," he said.

FBI personnel were assisting their Italian counterparts in the investigation, an FBI official said.

U.S. authorities had no intelligence suggesting any kind of terrorist attack was imminent in Milan, a U.S. official said.

On March 27, the State Department issued a warning for American citizens traveling in four Italian cities, including Milan, during Easter.

The warning said the possible threat was based on information about "extremist groups."

It was the second time since the Sept. 11 terror attacks that a plane has struck a high-rise building. On Jan. 5, a 15-year-old boy flying alone crashed a stolen plane into a building in Tampa, Fla.

The boy, Charles Bishop, left behind a suicide note saying that Al Qaeda terrorists had tried to recruit him, but police said there was no truth to the claim. Relatives of the boy, who was the only fatality, have filed a lawsuit claiming the acne drug Accutane was behind his suicide.

U.S. officials have called a mosque and cultural center in Milan "the main Al Qaeda station house in Europe."

Since Sept. 11, several individuals have been arrested in Milan as part of a crackdown on suspected Islamic militants. Italian authorities uncovered an alleged Al Qaeda plot in January, 2001, to attack the U.S. Embassy in Rome and are investigating whether a second plot was in the works earlier this year.

The Associated Press contributed to this report.