The height of the WAshington Monument was incorrect in a chart about the World Trade Center explosion yesterday. The monument is slightly more than 555 feet tall. (Published 2/28/93)

NEW YORK, FEB. 26 -- An explosion, possibly caused by a bomb, ripped through a hotel parking garage beneath the World Trade Center this afternoon, killing at least five people, injuring more than 500 and causing a frantic midday evacuation of tens of thousands of workers from the complex's twin towers.

The blast at 12:17 p.m. left a crater measuring at least 100-by-100 feet in the three-story garage, scattering concrete debris throughout an adjacent commuter-rail station and filling all 110 stories of one tower with smoke within minutes.

Authorities here said tonight that they had not determined the cause of the blast, although they said it was "possible" that it was caused by a bomb.

"I heard a boom," said Shannon Murphy, 24, who works for an accounting firm on the 101st floor of One World Trade Center. "It felt like thunder up there. You always feel it when it's windy. But this was different. I felt the floor move . . . . Within five minutes, there was smoke on our floor."

In Washington, John C. Killorin, spokesman for the Bureau of Alcohol, Tobacco and Firearms (BATF), said, "We are suspicious of what happened" and "are going to investigate it as a bombing." He said authorities are aware that "key evidence as to what happened is under rubble." No one, he said, "has the evidence in hand to say it was a bombing."

FBI bomb technicians and a special BATF team of explosives experts and forensic technicians were sent here tonight.

After New York Gov. Mario M. Cuomo (D) and Mayor David N. Dinkins (D) spoke late today with President Clinton about the explosion, White House press secretary Dee Dee Myers said New York authorities "have reason to believe it was a bomb but are not definite."

New York Police Commissioner Raymond W. Kelly said police received at least seven calls, apparently from different people, saying they were responsible for the blast after it occurred. "To the best of our knowledge," he said, "there were no calls before" the blast.

A federal law enforcement official speaking on condition of anonymity said at least nine such phone calls had been logged and that the first came within an hour after the explosion to a nonemergency police number. There were several reports that one caller used the phrase "Serbian Liberation Front," but U.S. officials said they knew of no such organization.

In an interview with reporters, Cuomo said he had been told that one caller identified himself as representing Croatian militants. There was no immediate confirmation of that call.

The explosion occurred in the parking garage of the Vista International Hotel, which abuts the twin towers and whose garage is directly beneath one tower. Firefighters said the blast appeared to have been centered near the edge of a ramp about 100 feet from the street entrance.

In that section of the garage, the Secret Service field office here, the agency's largest national field office, stores more than 100 of its cars, including armored vehicles. Dale Wilson, a Secret Service spokesman in Washington, said there was "no information" on which to conclude that the organization was a target of the explosion.

Three agents received "minor injuries from flying debris," and some cars were extensively damaged, Wilson said.

The suspected bombing precipitated an afternoon of sheer mayhem in Manhattan. Hours later, almost 50,000 people were evacuated from the Empire State Building after a bomb scare there. Officials also reported two bomb threats but no evacutions at the United Nations.

As many as 750 firefighters, 40 percent of the city's firefighting equipment and hundreds of other police and federal law enforcement officials descended on the Wall Street area around the trade center. Spokesman Frank McCabe of the New York Fire Department said 750 firefighters mark the equivalent of a 16-alarm fire.

The city's most crowded business district ground to a halt in dozens of blocks of traffic gridlock.

Throughout the afternoon and early evening, an estimated 50,000 people staggered onto sidewalks outside the massive complex, their faces and clothes blackened with soot. Many had spent hours slowly making their way from upper floors on crowded, smoky, often dark fire stairways.

"It felt like we were in there forever," said Nell Torres, 37, a trainee with Manufacturers Hanover Bank on the 51st floor. "My eyes were stinging, and I had difficulty breathing. But everybody was calm."

Fire and rescue workers emerging from the damaged underground tonight reported seeing a hole 100 feet in diameter at the level where the explosion occurred and holes through cement floors two stories up and two stories down. The Vista's banquet room two stories above the blast was filled with rubble from shattered walls and floors, and the ceiling and walls in the Port Authority Trans-Hudson (PATH) commuter-rail station two stories below were blown out, they said.

Firefighters described an almost surreal scene underground: steam pipes bursting, cars burning, concrete walls collapsing, support columns buckling and miles of electrical cables strewn randomly over floor and ceiling.

"Whatever it was, it was really big," said John Glidden, a firefighter from the 101 Ladder Company.

The fire apparently never spread beyond the basement area, and the most serious injuries occurred on the concourse level of the PATH station, officials said.

Federal law enforcement and antiterrorist officials said the force of the explosion, whatever the cause, was magnified because it was contained inside such a huge structure. Much of the force from a car bombing or outdoor explosion dissipates in the atmosphere, they noted. "No matter what caused this, it was a tremendous explosion," Killorin said.

Peter Hegyi, 24, a salesman for Lanier, a business systems company, said he saw one uniformed worker evacuated from the train station soon after the explosion with a three-inch bone exposed and penetrating the back of his jacket. Another train-station worker ran past Hegyi with the back of his jacket afire, he said, as other workers attempted to extinguish the flames. Hegyi also said he saw a uniformed worker with a severely lacerated face.

The blast shook almost all of the floors above it, and sent clouds of smoke billowing up ventilation and elevator shafts to the uppermost floors, officials and evacuated workers said.

"There was a big boom," said Joseph Bederi, 30, a gold trader. "I was very scared. People were stumbling out of their offices. It was like a movie."

The evacuation was entirely impromptu because no electrical and fire-alarm systems sounded in the building. Stanley Breznoff, executive director of the Port Authority of New York and New Jersey that owns the trade center, said tonight that the building's operations control center was just above the garage where the blast was centered.

"Everything was blown up," he said.

Some of the building's occupants remained stranded on the upper floors at nightfall as firefighters methodically combed the 4.1-million-square-foot complex floor by floor.

McCabe said that, as of 9:30 p.m., about 100 people remained on high floors of the towers. Eight disabled people were trapped on the 94th floor before they were taken to the roof and removed by helicopter, the last people out of the building, the Port Authority said.

Several dozen young schoolchildren and their adult monitors were on their way down from the observation deck atop the center when their elevator stopped above the 40th floor. Amid the confusion, Port Authority officers did not find the children in the elevator for five hours.

"Their spirits were better than those of the adults," said Officer Jack Myer, who helped to evacuate the children.

The children were from P.S. 95 in the Gravesend area of Brooklyn and two other elementary schools. Authorities said one group was trapped in the painful cold on the observation deck atop One World Trade Center tower for nearly three hours, afraid to come inside because of thick smoke in the building. Another group had to walk down from the roof, they said.

Another group of elementary schoolchildren was not found until 6 p.m. when firefighters encountered them on the 35th floor.

Most of the injured, including about 300 people were transported to three area hospitals by bus and a relay of city and suburban ambulances, suffered smoke inhalation during the trek down and were not in immediate danger, officials said.

Officials at New York Downtown Hospital, a quarter-mile from the scene, reported treating at least 139 victims, primarily for smoke inhalation but also for laceration and burns.

St. Vincent's Hospital in Greenwich Village reported receiving at least 103 patients, including one with a fractured hip and one with cardiac arrest. One was pronounced dead on arrival, officials said. At midtown's Bellevue Hospital, where patients were bused because of an ambulance shortage, two of at least 53 patients were reported in serious condition and one was in critical condition.

According to police, at least four of the dead were Port Authority employees. Their identities had not been made public last night.

The mess at the trade center also snarled traffic for miles around Lower Manhattan. Commuter train service from the Wall Street area to New Jersey was canceled. About 20 percent of subway operations in the area were halted, and two of the tunnels leading from New Jersey to Lower Manhattan were closed so emergency vehicles would have easier access to the center.

"Tens of thousands of motorists are totally disoriented right now," said Lucius Riccio, transportation commissioner. "Lower Manhattan is frozen."

Meanwhile in Washington, a Clinton administration official said an "explosive device" was found yesterday near the U.S. Embassy in Zagreb, the capital of Croatia, but did not detonate. It was discovered "several hours" before the New York explosion, and the two events are not believed to be related, the official said. "Bombs have been found from time to time in streets near the embassy," the official said.

The official said he did not know the type or potential intensity of the bomb, which was dismantled by Croatian police.

U.S. citizens have often been targets of terrorism abroad, but the number of terrorist acts reported in this country had declined from 51 in 1982 to four in 1989, FBI Director William S. Sessions reported in February 1990.

In March 1989, the wife of the captain of the USS Vincennes, which had shot down an Iranian passenger jet the previous year, escaped serious injury when the van she was driving in San Diego was destroyed by a bomb.

In 1983, a bomb exploded near the Senate chamber in the U.S. Capitol. A group called the Armed Resistance Unit said it planted the device, which caused no injuries.

A year earlier, police in Washington shot and killed a man who said that a van he had driven across the Mall to the entrance of the Washington Monument was packed with 1,000 pounds of explosives. No explosives were found.

Contributing to this report were staff writer Paula Span and special correspondents Julia Preston, Eleanor Randolph and Rachel E. Stassen-Berger in New York and staff writers George Lardner Jr. and Daniel Williams and staff researcher Mark Stencel in Washington.