Several thousand "Occupy Oakland" protesters on Wednesday night shut down the California city’s port, one of the busiest in the United States.

Some 5,000 people joined the protest, organizers said, in a strong start for the strike, called after police raided the group's downtown encampment last week and later clashed with protesters in teargas-choked streets.

The massive protest, which organizers claimed brought nearly 20,000 people onto the street in total, caused a number of businesses and banks to shut down.

"Our government is being bought by corporations," said Bruso, a Service Employees International Union member, told "The middle class and lower class are being subjugated.

He explained the shutdown of the Port of Oakland "sends a message to the corporate world that we're not going to sit by and take it anymore."

The vast majority of the protesters remained peaceful, but a small group of black bloc protesters defaced ATMs and broke windows at Wells Fargo, Bank of America and Chase Bank branches as the protesters marched through downtown, according to the Oakland Tribune.

A group of protesters also vandalized a Whole Foods store and someone spray-painted "fuck" on the side of the Christ the Light Cathedral.

There were no reports of arrests.

Mayor Jean Quan, criticized for her handling of the protests, issued a statement calling for calm -- and by early afternoon the mood remained peaceful.

"Police Chief (Howard) Jordan and I are dedicated to respecting the right of every demonstrator to peacefully assemble, but it is our duty to prioritize public safety," she said.

In contrast to last week, there was a minimal police presence.

Media reports and protest organizers claimed that work at the Port of Oakland was disrupted by strike action from early in the day, well ahead of the planned evening march on the port.

But a spokeswoman told AFP that the port was "open," and appealed for calm later in the day.

"Safety is the number one priority at the Port of Oakland, and we ask that everyone approach today with calm and respect," she said.

A statement added: "The Port of Oakland is open ... At the seaport, marine terminals are generally operating, although the situation is fluid.

"Each of our the Port's terminals operates independently, and Port staff are in close touch with terminal operators, shipping companies, and other tenants," it said.

The port would provide updates during the day, as the situation develops, said the spokeswoman.

Back in downtown, the mood among protesters in Oakland, outside San Francisco, was jubilant. "We're doing something that's never happened in history," said "occupier" Jedidiah Lee. "We're changing the world."

Lee, 29, said he had come across the bay from Occupy San Francisco, where protesters have pledged to support their Oakland counterparts in the strike.

As hundreds of protesters gathered en mass in a downtown intersection, a singer belted out, "I Will Survive."

The crowd then began to march down a major city street, hip-hop music blaring from speakers set up in the back of a pickup truck parked at the intersection.

Brother Muziki, an elementary school teacher, was helping carry a banner reading: "Bail out schools and services, not banks!"

"Our classrooms are overcrowded, he said. "The banks are being bailed out -- but not the schools."

Oakland Unified School District spokesman Troy Flint said some 268 teachers had requested substitutes for the day. But many more had also called in sick or not shown up, he said.

Flint said the district supported the strike's goals, which include fighting for more money for public education, and had worked with the teachers union to develop strike-related classroom curriculum for the day.

While the morning started off peacefully, police have raised concerns about potential violence as crowds swell. Most protesters advocate nonviolence but a minority support a more aggressive approach.

Two more marches, including an evening march to the Port of Oakland, were planned.

Watch video of the demonstration, courtesy of NBC Bay Area, below:

Watch video of the black bloc protesters, courtesy of NBC Bay Area, below:

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Photo credit: Twitter user @pixplz. Front page photo: astro twilight

With additional reporting by Raw Story

Updated 12:42 pm ET.