Police, some in riot gear, arrested at least one demonstrator on the Michigan Avenue Bridge after protesters swarmed the area, blocking traffic. One demonstrator was caught on video by WLS-TV, Chicago, tearing down one of the NATO welcoming signs on a bridge tower.
Demonstrators said police used a maneuver known as "kettling" to disperse the protesters, some of whom regrouped and headed toward the Federal Reserve Bank of Chicago, blocking intersections in the city's financial district.
Occupy Chicago posted messages on Twitter, urging demonstrators to converge on Mayor Rahm Emanuel's North Side home Saturday to demand "healthcare not warfare."
Earlier, nurses dressed in red shorts and green Robin Hood felt hats gathered on Daley Plaza, demanding a tax on financial institutions' transactions to fund healthcare and social services.
"We bailed them out. As nurses, we are concerned because our patients are doing without medication. They do not have jobs. We bailed out Wall Street. It's time for them to give back to us," Dorothy Higgins, a nurse from Half Moon Bay, Calif., told WBBM-AM, Chicago.
After the rally, demonstrators marched to the South Loop.
The rally organized by National Nurses United was to coincide with the Group of Eight Summit but the site of that meeting was switched to Camp David, Md. The NATO meeting begins Sunday.
Afghan President Hamid Karzai was among the first heads of state to arrive in Chicago. His motorcade shut down the Kennedy Expressway as he headed downtown from O'Hare International Airport.
Chicago is the first U.S. city outside of Washington to host a NATO summit and city officials said they hope the city will make a good impression, the Chicago Tribune reported Friday.
U.S. President Barack Obama was to arrive Saturday following the G8 meeting. His first meeting Sunday was to be with Karzai, Obama's security adviser said.
Emanuel said the cost of the event will be covered by a $19 million federal grant and $37 million in commitments from private donors, the Tribune reported.
Some businesses, concerned about possible violence by protesters, suggested their downtown employees work from home during the summit. Restaurateurs reported weekend bookings down markedly because of fears of violence.
Residents have been warned to expect traffic disruptions on expressways as motorcades move through the city. Some commuter rail stations have been closed and Metra passengers have been informed of tough restrictions on backpacks, food and other items.