The barrage of non-lethal objects, that also included bean bags, came at an early morning rally to protest the US invasion of Iraq and the alleged involvement of US corporations in encouraging the conflict, protesters said.

Officers opened fire to disperse a crowd of around 500 people picketing the docks of shippers American Presidents Lines at the port of Oakland in California as part of a nationwide civil disobedience campaign.

At least six people were injured in the incident, intended to protest an alleged contract the shipping line has won from the US government to ship war supplies to US-led forces in Iraq.

"Demonstrators were picketing legally to protest the war when police overreacted and began pelting them with rubber bullets and other objects without warning," said Patrick Reinsborough of Direct Action to Stop the War.

Among the injured were six longshoremen who were waiting to for the picket line to break up before entering the docks, said Steve Stallone of the International Longshore and Warehouse Union who was at the scene.

"The protest was totally peaceful," he said. "The police suddenly gave a two-minute warning for demonstrators to disperse and then began firing objects and grenades into the crowd.

"It was terrifying and as far as I could see there was absolutely no reason for them to resort to justice as protesters did move away from the gate when they were told to," Stallone told AFP.

Police said they had warned the protesters to clear the area around the port several times and that protesters had lobbed rocks and bolts at officers before authorities resorted to a barrage of non-lethal objects.

"Our intent out is to allow people to express their first amendment (freedom of expression) rights peacefully and within the law," Deputy Chief Patrick Haw said.

But demonstrators, who brandished placards bearing slogans that read "Shut down the war makers" and "Embargo war cargo" accused the officers of using excessive force.

"These are peaceful protesters being shot at by police," said demonstrator Bradley Angel.

Witnesses said some of the injured were bleeding, while others were bruised or developed welts after being hit by rubber pellets, dowels or bean bags.

The protest was part of a rash of similar demonstrations and acts of civil disobedience aimed at opposing the invasion of Iraq.

Protesters had also gathered outside government offices in nearby San Francisco to denounce the US action, while similar demonstrations were planned for New York and Washington.

The demonstrations were aimed at capping off four days of protests aimed at stopping the war," Reinsborough said.

"We want to draw the links between the war and some of the big corporations that are set to profit from it," he said.

"Behind this military crisis in Iraq is a deeper democracy crisis here in the United States. This war is being driven by corporations with undue influence over the government and its actions in Iraq."

SPACE.WIRE