OAKLAND, Calif. – Several thousand Occupy Wall Street demonstrators gathering in Oakland forced a halt to operations at the nation’s fifth busiest port Wednesday evening, escalating a movement whose tactics had largely been limited to marches, rallies and tent encampments since it began in September.

Police estimated that a crowd of about 3,000 had gathered at the Port of Oakland by about 5 p.m. Some had marched from the city’s downtown, while others had been bused to the port.

Port spokesman Isaac Kos-Read said maritime operations had effectively been shut down, and interim Oakland police chief Howard Jordan warned that protesters who went inside the port’s gates would be committing a federal offense.

In Philadelphia, protesters were arrested earlier Wednesday as they held a sit-in at the headquarters of cable giant Comcast.

One protester, Bri Barton, said she was there because the gleaming Comcast tower represents excessive wealth in a city with many blighted neighborhoods. “It’s hard for me to see this and that existing in the same city,” she said.

Military veterans marched in uniform in New York, angry at their dim job prospects.

And parents and their kids, some in strollers, formed a “children’s brigade” to join the Oakland rallies.

“There’s absolutely something wrong with the system,” said Jessica Medina, a single mother who attends school part time and works at an Oakland cafe. “We need to change that.”

In Los Angeles, New York and other cities, demonstrators held their own rallies in solidarity with the Oakland protesters, who called for Wednesday’s “general strike” after the city became a rallying point last week when an Iraq War veteran was injured in clashes with police.

Protesters, city officials and business leaders were optimistic the strike would be peaceful, and there was little to no visible police presence all day.

Although windows at two bank branches and a Whole Foods store were broken and graffiti was painted inside one of the banks, officials described the protests as peaceful and said no arrests had been made.

“It is important to acknowledge the world is watching Oakland tonight,” city administrator Deanna Santana said as demonstrators began to gather at the port. “And we need to ensure it remains a safe place for everyone.”

Potentially minimizing any serious disruptions at the port, leaders of the longshoremen’s union said they could not call for members to join the protests under their contract with the port.

Organizers say they want to stop the “flow of capital.” The port sends goods primarily to Asia, including wine as well as rice, fruits and nuts, and handles imported electronics, apparel and manufacturing equipment, mostly from Asia, as well as cars and parts from Toyota, Honda, Nissan and Hyundai.

Craig Merrilees, spokesman for the International Longshore and Warehouse Union, said its members were not being called to strike but that they supported the protesters.

The members “are supporting the concerns raised by Occupy Oakland and the Occupy movement to speak up for the 99 percent and against the corporate greed that is wrecking America,” Merrilees said.

In New York, about 100 military veterans marched in uniform and stopped in front of the New York Stock Exchange, standing in formation as police officers on scooters separated them from the entrance. On the other side were NYPD horses carrying officers with nightsticks.

“We are marching to express support for our brother, (Iraq war veteran) Scott Olsen, who was injured in Oakland,” said Jerry Bordeleau, a former Army specialist who served in Iraq through 2009.

The veterans were also angry that returned from war to find few job prospects.

“Wall Street corporations have played a big role in the wars in Iraq and Afghanistan,” said Bordeleau, now a college student. He said private contractors have reaped big profits in those countries.

The day’s events in Oakland began with a rally outside City Hall that drew more than 3,000 people who spilled into the streets and disrupted the downtown commute. Protesters hung a large black banner that read: “Occupy Everything, DEATH TO CAPITALISM.”

The crowd included students, families and many people wearing labor union T-shirts. “Shut down the 1 percent. We are the 99 percent,” they chanted.

Oakland let city workers use vacation or other paid time to take part, and officials said about 5 percent took the day off. About 360 Oakland teachers didn’t show up for work, or roughly 18 percent of the district’s 2,000 teachers, officials said. The district has been able to get substitute teachers for most classrooms, and where that wasn’t possible children were sent to other classrooms, he said.