NEW YORK, NY March 06, 2008 —NEW YORK (AP) - An explosive device caused minor damage to a landmark military recruiting station in Times Square before dawn Thursday, prompting a huge police response that disrupted transit at the "crossroads of the world."

No one was injured when the explosive went off about 3:45 a.m., police said. The blast left a gaping hole in the front window and shattered a glass door, twisting and blackening its metal frame.

Police said investigators would have to examine the evidence to determine what kind of device was used.

The center is normally staffed by two noncommissioned officers but was empty at the time of the explosion, said Capt. Charlie Jaquillard, the commander of army recruiting operations in Manhattan.

"If it is something that is directed toward American troops, then it's something that's taken very seriously and is pretty unfortunate," he said.

Members of the police department's bomb squad and fire officials gathered outside the recruiting station, which has occasionally been the site of anti-war demonstrations, ranging from silent vigils to loud rallies.

Police cars and yellow tape initially blocked drivers from entering one of the world's busiest crossroads, though some traffic was allowed through around the start of rush hour.

Guests at the Marriott Marquis on 46th Street said they heard a "big bang" and could feel the building shake. A large plume of smoke was also visible after the explosion, they said.

Terry Leighton, 49, from London, England, said he was on the 21st floor of the hotel when he heard the blast and looked out a window.

"I thought it could have been thunder," he said. "I looked down and there was a massive plume of smoke. So I knew it was an explosion."

Darla Teck, 25, was on the 44th floor of the hotel. "There was a big bang. I felt it," she said.

At one point in the investigation subway trains passed through the Times Square subway station without stopping, but normal service resumed with delays later in the morning. Police cars and tape blocked the streets.

The recruiting center has drawn sporadic protests for many years, including in October 2005, when a group who call themselves the Granny Peace Brigade rallied there against the Iraq war. Eighteen activists, most of them grandmothers in their 80s and 90s, were later acquitted of disorderly conduct.

The center was renovated in 1999 to better fit into the flashy ambiance of Times Square, using neon tubing to give the glass and steel office a patriotic American flag motif. For a half century, the station was the armed forces' busiest recruiting center. It has set national records for enlistment, averaging about 10,000 volunteers a year.

Police said it was too early to say if the blast may have been related to two other recent minor explosions in the city.

In October, two small explosive devices were tossed over a fence at the Mexican consulate, shattering three windows but causing no injuries. No threats had been made against the consulate, and no one took responsibility for the explosion, police said.

At the time, police said they were investigating whether it was connected to a similar incident at the British consulate on May 5, 2005.

In that incident, the explosions took place in the early morning hours, when Britons were going to the polls in an election that returned Prime Minister Tony Blair to power.

In both cases, the instruments were fake grenades sometimes sold as novelty items. They were packed with black powder and detonated with fuses, but incapable of causing serious harm, police said.

(Copyright 2008 by The Associated Press. All Rights Reserved.)