OAKLAND, Calif. -- Hundreds of Wall Street protesters blocked gates at some of the West Coast's busiest ports on Monday, causing the partial shutdown of several in a day of demonstrations they hope will cut into the profits of the corporations that run the docks.

The closures affected some of the terminals at the ports in Oakland, Calif., Portland, Ore., and Longview, Wash., though it was not immediately clear how much the shutdowns would affect operations and what the economic loss would be.

From California to as far away as Vancouver, British Columbia, protesters picketed gates, beating drums, carrying signs such as "Shutdown Wall St. on the Waterfront" and causing longer wait times for trucks.

There were a handful of arrests so far, but no major clashes with police.

While the demonstrations were largely peaceful and isolated to a few gates at each port, local officials in the union that represents longshoremen and, in some cases, port officials, determined that the conditions were unsafe for workers.

In Oakland, shipping companies and the longshoremen's union agreed to send home about 150 workers, essentially halting operations at two terminals. In Portland, authorities shuttered two terminals after arresting two people who were carrying weapons.

And in Longview, Wash., workers were sent home out of concerns for their "health and safety."

The movement, which sprang up this fall against what it sees as corporate greed and economic inequality, is focusing on the ports as the "economic engines for the elite" in its most dramatic gesture since police raids cleared out most remaining Occupy tent camps last month.

It was unclear whether demonstrators could amass in sufficient numbers to significantly disrupt or force more port closures as they did last month during an overnight shift at the Port of Oakland. The union that represents longshoremen says it doesn't support the shutdowns.

Protesters are most upset by two West Coast companies: port operator SSA Marine and grain exporter EGT. The bank, Goldman Sachs, owns a major stake in SSA Marine and has been a frequent target of protesters.

They say they are standing up for workers against the port companies, which have had high-profile clashes with union workers lately. Longshoremen at the Port of Longview, for example, have had a longstanding dispute with EGT.

In Oakland, officials urged protesters to consider the impact on workers. Port workers and truck drivers say the protests will hurt them.

Several hundred people picketed at the port before dawn and blocked some trucks from going through at least two entrances. A long line of big rigs sat outside one of the entrances, unable to drive into the port.

"This is joke. What are they protesting?" said Christian Vega, 32, who sat in his truck carrying a load of recycled paper from Pittsburg, Calif., on Monday morning. He said the delay was costing him $600.

"It only hurts me and the other drivers. We have jobs and families to support and feed. Most of them don't," Vega said.

Police in riot gear monitored the scene as protesters marched in an oval and carried signs. No major clashes were reported. Protesters cheered when they learned about the partial shutdown and they then dispersed. Another march on the port is planned later in the day.

The longshoremen's union said 150 workers were sent home after demonstrators blocked two entrances. Union spokesman Craig Merrilees said shipping companies agreed with workers' concerns about their safety. Those in unaffected parts of the port remained on the job.

"It's disappointing that those union folks were not able to go to work today and earn their wages," SSA spokesman Bob Watters said. He added: "We think that everything is pretty well in hand and operations are moving along pretty well now."

A message left with Bunge North America, EGT's parent company, was not immediately returned.

In Portland, Ore., a couple of hundred protesters blocked semitrailers from making deliveries at two major terminals. Security concerns were raised when police found two people in camouflage clothing with a gun, sword and walkie-talkies who said they were doing reconnaissance.

Port officials erected fences and told workers to stay home, port spokesman Josh Thomas said. He said port officials didn't know early Monday afternoon the full economic impact of the blockade.

"We're talking about tenants, customers, truckers, rail providers, a pretty far reaching group, and most of these people are not employed by the port," Thomas said. "To say it's going to be X amount of dollars right now is impossible."

Kari Koch, an Occupy spokeswoman, said the two people taken into custody were not part of the demonstration.

"We do not send out folks with guns," Koch said.

The decision to shut down the two terminals was relayed to about 200 workers from the longshoremen's union, which said it sympathized with the goals of the movement but disagreed with shutting down operations that would deprive its members of pay.

In Vancouver, demonstrators briefly blocked two gates at Port Metro Vancouver. The Canadian Press reported demonstrators held up a large banner proclaiming solidarity with longshoremen involved in the Port of Longview dispute.

The disruption lasted an hour before the protest moved to a second gate, blocking it for less than 30 minutes before moving on.

Longshoremen at the Longview port went home for the day over concerns for their health and safety, union spokeswoman Jennifer Sargent said. A port spokeswoman, Ashley Helenberg, said the both the port and the union made the decision.

Helenberg said about 20 shifts were affected. The port had one vessel to work on Monday.

Sargent said that if union workers participated in the protest, they did so as individuals, not as part of the union.

Organizers of the port demonstrations said they hope to draw thousands to stand in solidarity with longshoremen and port truckers they said are being exploited. The International Longshore and Warehouse Union, however, distanced itself from the shutdown effort.

The union's president suggested in a letter to members that protesters were attempting to co-opt the union's cause to advance their own.

Shutdown supporters said they're not asking longshoremen to organize a work stoppage in violation of their contract. They said they are simply asking them to exercise their free speech rights and stay off the job, in keeping with the union's historic tradition of activism.

If protesters muster large enough numbers to block entrances, arbitrators could declare unsafe working conditions. That would allow port workers to stay home.

Officials at West Coast ports said they have been coordinating with law enforcement agencies as they prepare for possible disruptions. Protesters said police crackdowns in any city will trigger an extension of blockades in other cities as a show of resolve.