Marchers briefly flooded the avenue and blocked traffic before police in riot gear pushed the crowd back onto the sidewalks. The group chanted: "We are the people. We are united!"
Earlier in the day, activists spread out over the city with Occupy members leading a charge against financial institutions. They faced police lined up in front of Bank of America on West 42nd Street and chanted: "Bank of America, bad for America!"
Julian Kliner, 22, said protesters' main issue with the banking giant is "how many people the Bank of America foreclosed as a result of predatory lending."
Organizers initially called for protesters to block one or more bridges or tunnels, but some protesters said later in the day those plans had been canceled. Occupy activists also had said they planned to bring business to a standstill on May Day. But there was no sign of any major disruption. Police said at least 15 arrests had been made by early afternoon.
May Day protests also took place Tuesday in Los Angeles, the San Francisco Bay Area, Chicago, Atlanta and other cities.
New York's May Day gatherings included nostalgia among those who participated in the Occupy protests last fall. Many gathering at Manhattan's Bryant Park hugged each other, recognizing faces they knew from Occupy's makeshift headquarters in Zuccotti Park.
Occupy organizer Mark Bray said the mood had changed since the group's first organized in September.
"There was a sense of novelty to Occupy in October," said Bray, 29, a Ph.D. history student at Rutgers University. "Today is more celebratory, and nostalgic."
With Zuccotti Park now empty of encamped protesters, "people still feel the need for that kind of space," he said. "I think the Zuccotti experience touched people - the experience of being there and having a cultural and political outlet."
The city broke the Zuccotti camp up in November, citing sanitary and other concerns, but the movement has held smaller events and protests periodically since then. Tuesday morning, nearby Wall Street was heavily barricaded as office workers streamed by on their way to work.
About 300 teachers and students skipped high school and college classes to hold activist teach-ins in Manhattan's Madison Square Park, Bray said. Earlier, more than 100 protesters walked over the Williamsburg Bridge and filed into a park on the Lower East Side.
After police forced marchers from the street onto the sidewalk, some responded by sprinting away from police, knocking over chairs, garbage cans and throwing cans into the middle of the streets. They threw police barricades into the middle of Broadway in an attempt to impede traffic.
John Connors, 31, a financial analyst and Occupy supporter, took the day off, as well as his shirt, revealing his chest with the words "Black Hole of Finance" painted on it.
Letters containing a white powder that appeared to be corn starch were sent to some institutions. Two letters were received Tuesday at News Corp. headquarters - one addressed to the Wall Street Journal - and a third was delivered to Citigroup. Their message said: "Happy May Day."
Seven letters were received Monday at various banks and one to Mayor Michael Bloomberg.
"This is a reminder that you are not in control. Just in case you needed some incentive to stop working," the letters read, according to authorities.
A group also picketed outside New York University to protest the university's expansion plans in Greenwich Village.
Over 30 protesters were arrested in the May Day protests, mostly for disorderly conduct and resisting arrest.
After the march down Broadway, a large number of protestors gathered at Vietnam Veteran's Plaza near 55 Water Street. The park closed at 10pm. Police advised people to clear out, and it the protesters did orderly.
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