NEW YORK (AP) -- Hundreds of Occupy Wall Street protesters and their supporters spilled out onto Fifth Avenue in a confrontation with police Tuesday amid a citywide day of May Day protests the group had promised would mark a spring revival of their movement.
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 business disruptions. Police said more than 30 arrests were made around the city, for such infractions as disorderly conduct.
May Day protests also took place Tuesday in Los Angeles, the San Francisco Bay Area, Chicago, Atlanta and other cities.
In New York, they involved an array of groups and included supporters of immigrants, labor unions and the Occupy movement. Some wore "Justice for Trayvon Martin" shirts.
In the afternoon, several thousand people converged on Manhattan's Union Square with signs, bullhorns and other paraphernalia. Some chanted at passers-by, while others relaxed on picnic blankets in the sun. Through loudspeakers, protest organizers called for an end to corporate greed, housing foreclosures, and war.
The May Day gatherings included nostalgia among those who participated in the Occupy protests last fall. Many at Manhattan's Bryant Park hugged each other, recognizing faces they knew from Occupy's now-dismantled headquarters in Zuccotti Park.
Occupy organizer Mark Bray said the mood had changed since the group's first organized events late last year.
"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."
But 22-year-old Sophia Clark said she believed the loss of Occupy's encampment had ultimately strengthened the movement.
"It just underscores the way people are not being heard," said the Sarah Lawrence College student. "Taking away Zuccotti Park was just underscoring how the system doesn't work."
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, with many members promising a warm-weather resurgence. Tuesday morning, nearby Wall Street was heavily barricaded as office workers streamed by on their way to work.
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.
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.
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.
Associated Press writers Meghan Barr, Samantha Gross and Colleen Long and Associated Press videographer Bonny Ghosh contributed to this report.