At 7:40 p.m. Wednesday, about 200 protesters surged toward a white pickup truck driven by a longshoreman trying to make his way home from the Port of Oakland.

With the worker surrounded at Maritime Street and Middle Harbor Road, some protesters began to beat on the truck. Others chanted, “Peaceful, peaceful,” until the group let the man go.

By then, Occupy Oakland, a movement that has expanded to include thousands of union members, students and teachers, had achieved its most ambitious goal yet: shutting down the nation’s fifth-busiest port and stalling millions of dollars in commercial activity.

Port officials closed the facility in the late afternoon, after thousands of protesters walked and bicycled one mile from City Hall to the front gates. With police largely absent, the marchers surged into the port itself, merrily scrambling over cargo containers and picnicking on the wharf.

The largely peaceful day ended in confrontations between protesters and police, with officers firing tear gas and making dozens of arrests downtown after midnight.

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The day's protest at the port kept out 200 longshoremen scheduled to work the overnight shift, delayed at least six cargo ships crammed with material and threatened to force incoming ships into staging areas near the Bay Bridge and other locations on San Francisco Bay.

At least seven ships were scheduled to dock by Thursday afternoon. It was unclear how many of the delayed outgoing ships contained perishable material; some $3.2 billion worth of fruits and nuts left the Port of Oakland last year, its largest export.

In a statement, the port said it hoped it could resume normal operations on Thursday.

“Continued missed shifts represent economic hardship for maritime workers, truckers, and their families, as well as lost jobs and lost tax revenue for our region,” the statement read.

City and port officials worried that small groups of protesters could cause trouble overnight and prevent the port from reopening in time to allow workers to begin their 8 a.m. shift.

“It’s OK for now but if it goes on for a couple days it could be a mess,” said one official familiar with the port operations.

The closure was a significant show of strength for Occupy Oakland, which has become an inspiration for the larger Occupy Wall Street movement since images of police officers launching tear gas and other objects at protesters last Tuesday near Oakland’s Frank H. Ogawa Plaza flashed across the globe.

“It looks like this was a good day for the 99 percent,” said Oakland Mayor Jean Quan, who has sought to align herself with the movement, even though hundreds of marchers carried signs calling for her resignation.

For the most part, protesters policed themselves. Police, who have been at odds with Quan throughout the crisis, were ordered to keep their distance, some waiting in vans to be used in mass arrests. There were none the entire day, even after four banks and a Whole Foods supermarket were vandalized with broken windows and graffiti.

Interim Oakland Police Chief Howard Jordan said that at its height, the protest “far exceeded our ability to manage a particular crowd control situation.” He estimated 7,000 demonstrators took to the streets.

Council member Jane Brunner, who marched with the protesters from Frank Ogawa Plaza to the port, said she felt the low numbers of police had kept the crowd more peaceful.

“The police are good guys, they’re part of the 99 percent, too,” she said. “But when they come out with their helmets, and their night sticks, they can look intimidating.”

The Port of Oakland was a big target for Occupy Oakland, an international cargo hub and the fourth-busiest container port in the United States, loading and discharging more than 99 percent of the container goods that pass through Northern California. Anywhere from a half dozen to more than 25 cargo ships enter and leave the port each day.

Throughout the evening Thursday, there were short, sometimes-tense standoffs between protesters and workers trying to leave the port.

Shortly after 8 p.m., as another group of protesters marched in a circle at the port, another worker drove up in a pickup truck and said he would not cross the picket line, even though it would cost him $565 to miss his shift.

The man, who gave only his first name, Juan, told the protesters: “Without you, there’s no me.”

In anticipation of the shutdown, port officials sent most employees home in the early afternoon. More delays were expected; six departures were scheduled from midnight to 7 a.m., according to a daily schedule compiled by the San Francisco Bar Pilots.

Port officials anticipated that arrivals would also be delayed indefinitely. One ship, the Horizon Eagle, was scheduled to dock at Berth No. 22 at 2 a.m., but the berth was occupied by another ship delayed by the protest.