Associated Press WriterMILAN, Italy (AP) -- A small plane with only the pilot on board crashed Thursday into a 30-story landmark skyscraper, killing at least two people and injuring at least 30. The interior minister said the crash appeared to be an accident.

It was the second time since the Sept. 11 terror attacks that a plane has struck a high-rise building, and Thursday's crash raised fears of another attack. "It sounded like a bomb. The pavement shook like an earthquake," said a woman identifying herself only as Lucia.

The Piper aircraft, en route from Switzerland on a 20-minute flight to Milan, punched a hole in the 25th floor of building in downtown Milan. Smoke poured out of the building, but firefighters quickly put out the flames. Rescuers helped bloodied men in business suits.

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" as the cause, the Italian news agency ANSA quoted Interior Minister Claudio Scajola as saying.

The pilot had sent out a distress call at 5:54 p.m. just before the crash near Milan's main train station, said police officer Celerissimo De Simone. RAI state TV reported that the pilot said the SOS was because of engine trouble.

"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, told AP that the plane left Locarno at 5.15 p.m.

ANSA said two were reported dead and that an unspecified number of people were rescued from elevators blocked in the building.

An office worker who fled told The Associated Press that she saw 10 people injured and bleeding. She worked on eight floor, well below the crash. 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, works in a skyscraper 500 yards from building. "The clock fell to the floor."

The scene in Milan mirrored the first moments of the attack on the World Trade Center, with black smoke billowing into the blue sky from the building where the aircraft struck. On the streets, rescue workers in orange uniforms helped the injured -- including a man with a bloody shirt holding his head. 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 people gawked at the skyscraper.

National Security Adviser Condoleezza Rice and White House chief of staff Andrew Card broke the news 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 on condition of anonymity.

U.S. authorities had no intelligence suggesting any kind of terrorist attack was imminent in Milan, said a U.S. official, also speaking on the condition of anonymity.

Milan was home to an al-Qaida cell that had plotted to attack the U.S. embassy in Rome in early 2001, but the cell was believed to have been broken up by arrests. The leader, Essid Sami Ben Khemais, was arrested in April 2001. Khemais also had met with Mohammed Atta, the lead hijacker in the Sept. 11 attacks, before his arrest.

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."

The announcement did not identify the groups or elaborate on the nature of the threats, but it warned that "these groups do not distinguish between official and civilian targets."

A U.S. official said the warning was based on very specific information that was "developed in very close cooperation with Italian authorities." Italian anti-terrorism officials refused to comment.

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-Qaida 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.

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, formally known as the Pan Am building.

U.S. officials have called a mosque and cultural center in Milan "the main al-Qaida 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 allegedly uncovered an al-Qaida 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.