CHICAGO (AP) – Dozens of protesters broke through a security fence near the site of the Democratic National Convention on the opening day on Monday, when thousands took to the streets to express their opposition to the war in Gaza.

Families with babies in strollers, students, elected officials and others holding signs and flags joined the march to the United Center, where the convention is being held, to demand a ceasefire in the war between Israel and Hamas. While the larger group marched peacefully, a few dozen who broke away tore down sections of the security fence.

Several protesters who managed to get through the fence were arrested and handcuffed by police. Officers put on gas masks as some protesters attempted to tear down a second fence in front of police. Authorities said the internal security perimeter around the convention grounds had not been breached and that there was no danger to convention attendees.

Chicago Police Chief Larry Snelling said some of the protesters who tore down the fence threw water bottles and other objects at police. Police deescalated the situation without using batons or chemicals, he said.

“If people want to enter a crowd and commit acts of violence or vandalism, we will stop them,” said Snelling, who walked in front of the protesters in a group of officers on Monday. “We will not tolerate anyone destroying things in our city.”

Members of the crowd chanted “End the occupation now” and then “The whole world is watching!” just like the anti-Vietnam War protesters during the infamous congress of 1968 in Chicago, as police clashed with protesters on live television. Families gathered on their porches and outside their doors as protesters marched by. Some children wore keffiyehs, blew bubbles or held up “free punches” signs.

The march came just as President Joe Biden, who has faced heavy criticism from pro-Palestinian groups, including the protesters, was walking around the largely empty United Center. Biden was scheduled to address the party that evening.

“Biden, you can’t hide. We accuse you of genocide,” the protesters chanted amid drumbeats. They also called him “Genocide Joe” and directed similar slogans at Vice President Kamala Harris.

Protesters said their plans had not changed since Biden left the race and the party quickly gathered behind Harriswho will formally accept the Democratic nomination this week. Activists said they are ready to spread their progressive message to the country’s top Democratic politicians.

“People are dying,” said Cameron Benrud, a 25-year-old high school special education teacher from Minneapolis who drove five hours to attend the rally in Union Park to call on Democratic politicians to stop funding Israel.

“I’m from little old Minnesota, and you kind of feel powerless… You have to do something,” he said.

Mayor Brandon Johnson said authorities were well prepared. “The city of Chicago is really good at these things,” he said at a press conference. “We are ready.”

Organizers had hoped that at least 20,000 people would attend Monday’s rally and march, but only a few thousand people appeared to turn out, although city officials declined to provide estimates of the number of participants.

“We are proud of the participation, especially given the extent of the repression by the city,” said organizer Faayani Aboma Mijana.

The Chicago area is home to one of the largest Palestinian communities in the country, and buses brought activists from across the country.

Taylor Cook, an organizer with the Freedom Road Socialist Organization, flew in from Atlanta to attend the march. Cook said the group is urging all Democrats to call for an end to aid to Israel, with a particular focus on Harris.

“We’re telling Kamala she’s complicit in this. People think it’s just Joe Biden, but she’s vice president,” Cook said. “So we’re saying you have to stop doing this if you want our vote.”

Medea Benjamin, who traveled to Chicago from Washington, DC with a female-led group of protesters calling for peace, said she was shocked that the Biden administration recently approved another $20 billion worth of arms sales to Israel.

“There is an incredible discrepancy between what the people of this country are demanding and what the government is doing,” she said before the rally in Union Park. “It disgusts us so much.”

Pro-Palestinian supporters flocked to the rally in the park west of the Loop business district.

Before the march, the independent presidential candidate Cornel West spoke to the crowd, who greeted him with cheers.

“This is not about Machiavellian politics or utilitarian electoral calculations,” he yelled into a microphone. “This is about morality. This is about spirituality.”

During the rally, about 40 pro-Israel supporters walked through the park. They remained mostly silent and waved Israeli flags. They were accompanied by about 20 police officers on bicycles. Although tensions arose at times, there were no physical confrontations.

Josh Weiner, co-founder of the Chicago Jewish Alliance, who marched with the pro-Israel group, said their intention was to “make our presence felt.” He said the group had applied for permits that were not approved by the city.

“The pro-Palestinian protesters have received several permits, including one for a march, although it seems to be a little one-sided,” Weiner said.

Coalition activists and the city disagree over the location of the protests and other logistical issues. A judge ruled in favor of the city’s one-mile march route, which organizers said was not long enough for the expected crowds.

Not a single speaker or audience member showed up on the podium provided by the city government near the United Center. Eight groups with a progressive agenda had signed up to speak for 45 minutes on Monday. On other days, some conservative groups, including the Illinois Policy Institute think tank, have scheduled talks.

In the afternoon, the Philadelphia-based Poor People’s Army, which advocates for economic justice, set up camp in Humboldt Park in the northwest of the city before marching more than three miles to the United Center.