Celebrations in New York City and Washington, D.C., began mere seconds after the death of al-Qaeda leader Osama bin Laden was announced.

Chants of "U.S.A.! U.S.A.!" soon rose up at Ground Zero in New York City, where the World Trade Center once stood, and outside the White House in Washington, D.C.

Thousands are still gathered at the White House. Some climbed trees for a better view of the swelling crowds.

At Ground Zero, the celebrations are even more emphatic.

Thousands of tourists and New Yorkers alike gathered at the site, cheering, taking pictures and toasting the news of bin Laden's death.

"N.Y.C.! N.Y.C.!" people chanted.

A firefighter waves to the crowd as people celebrate after al-Qaeda leader Osama bin Laden was killed in Pakistan, during a spontaneous celebration in New York's Times Square on Monday. (Chip East/Reuters)

CBC reporter David Common said from New York that the crowd at Ground Zero had thinned out by 6 a.m. Monday — the news broke late Sunday — but that the crowd was celebratory.

"For a decade…this was a site for mourning, for people to come on the anniversary, bagpipes were played, Amazing Grace," Common said. "And now it is a completely different air — it is one of celebration, of revelling, of people feeling that they've scored a victory."

The crowd includes people who live nearby, emergency response workers, and survivors of the attacks. "A lot of them are just everyday New Yorkers," he said. "I was out in the streets at 2 and 3 a.m. this morning, and there were just people running up and down the streets, looking at their cellphones, hearing about the news for the first time — very, very happy."

New York Mayor Michael Bloomberg said bin Laden's death is a victory that won't lessen the pain for victims' families but could allow for some closure for victims. Police Commissioner Ray Kelly had similar comments, but noted that police are in a heightened state of vigilance for any retaliation attacks.

Americans do not believe that the threat against the city has changed, Common said. Bin Laden's death came exactly a year after an attempted Times Square car bombing.

There is an added police presence in the city. Dozens of police cars and a couple of hundred officers are in the Ground Zero area, Common said.

Americans celebrate outside the ABC studio in New York's Times Square as news of Osama bin Laden's death is announced on the ticker, Monday, May 2, 2011. Mary Altaffer/Associated Press

"We've been waiting a long time for this day," Lisa Ramaci, a New Yorker whose husband was a freelance journalist killed in the Iraq war, said early Monday. "I think it's a relief for New York tonight just in the sense that we had this 10 years of frustration just building and building, wanting this guy dead, and now he is, and you can see how happy people are."

She was holding a flag and wearing a T-shirt depicting the Twin Towers and, in crosshairs, bin Laden. Nearby, a man held up a cardboard sign that read, "Obama 1, Osama 0."

Tabloid newspapers in New York had such headlines as "Got Him!" and "Rot in Hell."

Bin Laden was slain in his luxury hideout in Pakistan, early Monday local time and late Sunday night in the United States, in a firefight with American forces. Obama said no Americans had been harmed in the operation.

As news of the president's announcement began to filter across the country, the New York Mets and Philadelphia Phillies were in the middle of a game in Philadelphia, and chants of "U.S.A.! U.S.A.!" began in the top of the ninth inning at Citizens Bank Park. Fans could be seen all over the stadium checking their phones and sharing the news.

A large, jubilant crowd reacts to the news of Osama bin Laden's death near Ground Zero, during the early-morning hours Monday in New York. Jason DeCrow/Associated Press

"U.S.A." chants echoed in Dearborn, Mich., a heavily Middle Eastern suburb of Detroit, where a small crowd gathered outside City Hall and waved American flags. Across town, some honked their car horns as they drove along the main street where most of the Arab-American restaurants and shops are located.

At the Arabica Cafe, big-screen TVs that normally show sports were all turned to news about bin Laden. The manager there, Mohamed Kobeissi, said it was finally justice for the victims.

There were smaller, spontaneous gatherings around the U.S., including a handful of Idahoans who made their way to the state Capitol in downtown Boise and a small group of people who waved flags and cheered on an Interstate 5 overpass south of Seattle known as Freedom Bridge.

With files from The Associated Press