CHICAGO — Protesters broke through a fence set up by police near the site of the Democratic National Convention on its opening day Monday as thousands took to the streets to voice their opposition to the war in Gaza.

As the larger group marched, a few dozen who broke away tore down pieces of the security fence. Some protesters, dressed in black with their faces covered, dragged pieces of the fence back to a park near the United Center, where the convention is being held.

Several protesters who had managed to get through the fence were detained and handcuffed by the police.

Authorities said the inner security perimeter surrounding convention site was not breached and there was no threat to those attending the convention.

Members of the crowd chanted “End the occupation now” and then “The whole world is watching!” just as anti-Vietnam War protesters did during the infamous 1968 convention in Chicago when police clashed with protesters on live television. Officers put on gas masks as some protesters tried to bring down a second fence set up in front of police.

The march happened just as President Joe Biden, who has been the target of intense criticism from pro-Palestinian groups, including the marchers, was doing a walk-through of the largely empty United Center. Biden was scheduled to address the party in the evening.

“Biden, you can’t hide. We charge you with genocide,” the marchers chanted amid the beating of drums. They also referred to him as “Genocide Joe” and lodged similar chants at Vice President Kamala Harris.

Protesters said their plans have not changed since Biden left the race and the party quickly rallied behind Harris, who will formally accept the Democratic nomination this week. Activists said they were ready to amplify their progressive message before the nation’s top Democratic leaders.

“We have to play our part in the belly of the beast to stop the genocide, to end U.S. aid to Israel and stand with Palestine,” said Hatem Abudayyeh, a spokesperson for the Coalition to March on the DNC, which includes hundreds of organizations.

The heavy police presence at the march included Chicago Police Superintendent Larry Snelling, who walked in a group of officers ahead of the protesters.

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

Organizers had hoped at least 20,000 people would take part in Monday’s rally and march, but it appeared that only a few thousand were present when the march began, though city officials declined to give a crowd estimate.

“We’re proud of the turnout, especially considering the degree of the repression from the city,” said organizer Faayani Aboma Mijana.

The Chicago area has one of the largest Palestinian communities in the nation, and buses were bringing activists from all over the country.

Taylor Cook, an organizer with the Freedom Road Socialist Organization, traveled from Atlanta for the march. Cook said the group was pushing all Democrats to call for an end to aid to Israel, with a particular focus on Harris.

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

Medea Benjamin, who traveled to Chicago from Washington, D.C., with a women-led group of protesters calling for peace, said she was shocked that the Biden administration recently approved an additional $20 billion in weapons sales to Israel.

“There’s an incredible discrepancy in what people are calling for in this country and what the administration is doing,” she said ahead of the rally in Union Park. “We’re so disgusted by this.”

Pro-Palestinian supporters descended on the park, west of the Loop business district, for the rally.

Prior to the march, independent presidential candidate Cornel West addressed the crowd, which welcomed him with cheers.

“This is not about some Machiavellian politics or some utilitarian calculation about an election,” he yelled into a microphone. “This is about morality. This is about spirituality.”

Around 40 pro-Israel supporters walked around the park during the rally. Remaining mostly silent while waving Israeli flags, they were accompanied by about 20 police officers on bicycles.

Although tensions flared at times, there were no physical altercations.

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

“The pro-Palestine protesters have gotten multiple permits, including a march, which seems to be a little bit weighted on one side,” Weiner said.

Some businesses boarded up their windows as a precaution, and county courts said they would open more space in case of mass arrests. Chicago police say officers have undergone extensive training on constitutional policing and de-escalation tactics.

Progressive activist Cornel West gestures during a demonstration prior to a march to the Democratic National Convention Monday, Aug. 19, 2024, in Chicago. (AP Photo/Alex Brandon)