By Jonathan Allen
NEW YORK (Reuters) - A million people are expected to gather in Times Square on Saturday to watch the ball drop on 2011, a year marked by the 10th anniversary of the September 11 attacks, and usher in a new year that includes a U.S. presidential election.
New York police began to close off streets on Saturday afternoon around Times Square, where amid tight security revelers will watch a lighted crystal ball descend for the last minute of 2011 in a tradition started in 1907.
The light-studded ball is raised six hours before the drop, followed by dance performances and handouts to revelers who police will bar from carrying alcohol, backpacks, large bags or packages into the square.
The raucous celebration is scheduled to include appearances by pop stars Justin Bieber, Lady Gaga and Cee Lo Green among others whose live performances in the square are broadcast across the nation leading to the main event.
Police spokesman Paul Browne said the city was expecting about a million visitors in Times Square on Saturday night, drawn in part by relatively mild weather. The National Weather Service forecast a low of about 40 degrees Fahrenheit.
He said bomb squad units would be conducting sweeps of hotels, theaters, construction sites and parking garages.
"New York City is always at the top of the terrorists' target list and we treat most large gatherings, especially high profile, iconic ones like New Year's Eve, as potential targets," Browne said in an e-mail. "However, there are no known threats on the city coinciding with New Year's Eve."
Radiation-detection boats would also be deployed in the city's waterways, where 33 dinner cruises were scheduled to take place on Saturday night, and officers will patrol the city's streets and transit system, Browne said.
A little more than two hours before the new year, New Yorkers will toast to the memory of those who died in the September 11, 2001, attacks on the World Trade Center. Somber ceremonies marked the 10th anniversary of those attacks in September.
That comes after 2011 saw U.S. forces kill al Qaeda leader Osama Bin Laden, the mastermind behind the September 11 attacks, in a raid in May on a large compound where he was staying in Pakistan. The year also saw the last of U.S. troops withdraw from Iraq in mid-December although they remain in Afghanistan.
At one minute before midnight, New York Mayor Michael Bloomberg and singer Lady Gaga are scheduled to press the button that signals the 60-second descent of the Waterford crystal ball.
The dropping of the 11,875-pound ball, studded with more than 32,000 LED lights, from its perch above Times Square is televised around the world. The streets around Times Square are expected to be cordoned off by police until about 3 a.m. on Sunday.
(Reporting by Jonathan Allen and David Bailey; Editing by Cynthia Johnston)