The parade set off from the southern tip of Manhattan and moved slowly north to City Hall as fans stood dressed head-to-toe in Giants gear and confetti wafted slowly down from the high-rises that line the street.
Manning, joined by coach Tom Coughlin, Bloomberg, Gov. Andrew Cuomo and other teammates, waved and grinned from the float as a deep roar rose from the crowds.
Bloomberg asked: "Are you feeling `deja blue' all over again?" referring to the team's 2008 win against the New England Patriots. The crowd cheered.
"The key thing was to remember this: All things are possible for those who believe," Coughlin said. "We always believed."
Some fans waited since 6 a.m. to catch a glimpse of their favorite players. About half of a Long Island high school class skipped school to see "a whole nation coming together in one place - this parade," said Mike King, 16, of Wantagh, N.Y.
King and seven school friends got up at dawn, arriving by subway in lower Manhattan to join the crowds packed behind police barricades lining Broadway. He attributed the win to the stellar performance of Manning and the hold-your-breath catch by Mario Manningham that led to the game-winning drive.
Frank Capogrosso, 11, from Staten Island, with his dad and his best friend, standing at this beginning of parade route, leaning against the barricade with a grin on his face.
"This is better than TV. I love the cop cars, the toilet paper, and the ecstatic fans." He added: I'm ecstatic. I love the Giants, I love their style: They play, they don't talk."
The parade for the Super Bowl champions will have an estimated economic impact of up to $38 million for the city, depending on the number of spectators, Bloomberg said. As many as 1 million are expected - about a third of them from outside New York.
After the parade, the team will travel to New Jersey for a 3 p.m. rally at MetLife Stadium.
But it's hard to imagine a victory more exciting than the Giants' last-minute 21-17 victory over the Patriots. The hero of this year's parade undoubtedly will be Super Bowl MVP Manning. Manning and Manningham connected on the clutch play, as the receiver made the over-the-shoulder catch along the sideline.
From a Broadway high-rise older than the ticker-tape tradition, members of the law firm Kenyon & Kenyon dumped shredded paper out their windows to the spectacular view below of the lauded athletes.
Jun Kim, 28, a Korean linguist, reserved his biggest batch for Manning. "You are a star!" he yelled as the quarterback passed by. "People thought he would crumble under pressure, but he didn't. He's the best."
New York City Sanitation Commissioner John Doherty said he expected to see about 40 tons of paper showered down. That's a lot but not one for the record books. The city threw 5,438 tons of ticker tape on returning veterans at the end of World War II in 1945.
Even before the parade started, city sanitation crews with hand-held vacuums were ready to suck up the piles of confetti that would rain on Broadway.
The second-highest amount of paper was thrown to honor astronaut John Glenn in 1962 - 3,474 tons. The actual ticker tape from those days has been replaced by recycled paper that's shredded into confetti.
Sanitation spokeswoman Kathy Dawkins says the department picked up 34.2 tons of paper after the Giants' last parade in 2008.
The streets Tuesday were a mass of metal police barricades, and security was tight with helicopters flying overhead and police command centers parked nearby.
Sanitation worker Joey Lobosco, 38, from Staten Island, cheered as the team passed by.
"I like the whole atmosphere here - of winning in New York - there's nothing like it. Winning in the greatest city in the world," Lobosco said.
Mindy Forman, 53, of Yorktown, N.Y., was one of the lucky few who scored a ticket to the festivities at City Hall. She said the win was a much-needed victory at a time when many could use some cheering up. She counted herself among that group: She was laid off two weeks ago from her job as a college administrator.
"It celebrates New York," she said. "It celebrates the city. It celebrates the state. And it gives people something to believe in in very hard times."
New York has feted its public heroes since 1919, with the first parade for World War I General John Pershing and his victorious troops.
They were followed by more than 200 parades honoring such people as aviator Charles Lindbergh, scientist Albert Einstein, Pope John Paul, South African leader Nelson Mandela and pianist Van Cliburn. Their names are chiseled into the Broadway sidewalks.
Associated Press Writer Samantha Gross contributed to this report. She can be reached at www.twitter.com/samanthagross