NEW YORK -- An Oregon woman staying at a Marriott hotel four blocks from Times Square in New York said she could feel the building shake during an explosion nearby Thursday morning.

"It was a big bang," she said.

An explosive device caused minor damage to an empty military recruiting station in Times Square and authorities are trying to figure out who was behind it.

Darla Peck, of Portland, was up on the 44th floor of at hotel in "the crossroads of the world" and could feel it.

 More: Details on Times Square blast investigation

The blast left a gaping hole in the front window of the recruiting center and shattered a glass door, twisting and blackening its metal frame just after 4 a.m.

"It shook the building. I thought it could have been thunder, but I looked down and there was a massive plume of smoke so I knew it was an explosion," said Terry Leighton, 48, of London, who was staying on the 21st floor of the same hotel as Peck.

Mayor Michael Bloomberg said the act "insults every one of our brave men and women in uniform stationed around the world." "Whoever the coward was that committed this disgraceful act on our city will be found and prosecuted to the full extent of the law," said Bloomberg. "We will not tolerate such attacks."

No one was inside the station, where the Marines, Air Force and Navy also recruit.

Authorities said at a news conference that a witness saw a person on a bicycle wearing a backpack and acting suspiciously, but that no one saw a person place the device in front of the recruiting center.

"If it is something that's directed toward American troops then it's something that's taken very seriously and is pretty unfortunate," said Army Capt. Charlie Jaquillard, who is the commander of Army recruiting in Manhattan.

Members of the police department's bomb squad and fire officials gathered outside the station in the early morning darkness, and police cars and yellow tape blocked drivers -- most of them behind the wheels of taxicabs -- from entering one of the world's busiest crossroads. Police began allowing some traffic through around the start of rush hour.

Though subway cars passed through the Times Square station without stopping in the early hours of the investigation, normal service was soon restored, with some delays. The recruiting station, located on a traffic island surrounded by Broadway theaters and chain restaurants, has occasionally been the site of anti-war demonstrations, ranging from silent vigils to loud rallies.

FBI offers reward in Oregon bomb hoax probe

FBI agents are currently investigating a series of bomb hoaxes at military recruiting centers in Oregon. The incidents date back to March 2007 and include threats in Portland and Salem.