At least nine demonstrators and bystanders were injured as police fired non-lethal ammunition to disperse the demonstrators the port of Oakland in California, they said.

Police said that around 30 protesters were arrested in the early morning skirmish which marked the first time police had opened fire on US anti-war demonstrators since the invasion of Iraq began on March 20.

Demonstrators and port workers said the police opened fire on the early morning picket line without warning or provocation as protesters blocked the entrance to the docks of American President Lines.

Anti-war groups allege that APL has won a US government contract to ship war supplies to forces in Iraq.

Between 500 and 750 protestors blocked gates of the pier brandishing placards bearing slogans that read "Shut down the war makers" and "Embargo war cargo."

"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.

"The protest was totally peaceful," said Steve Stallone of the International Longshore and Warehouse Union who was at the scene.

"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.

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 injured included nine port workers who were standing well away from the pickets, said Henry Graham, president of the local branch of the International Longshore and Warehouse Union.

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

"The city of Oakland will not tolerate attacks, which jeopardize the safety of our citizens, businesses, police officers and law-abiding protesters," police said in a statement.

"As a result of the unlawful acts of individuals and their continued refusal to disperse, various crowd dispersal devices ... were deployed."

But protestors, city officials and port workers at the scene said the demonstration was entirely peaceful. Deputy Oakland mayor Nancy Nadel said one of her aides at the scene witnessed no provocation by the picketers.

Demonstrator Scott Fleming, who was hit by police projectiles five times, said the officers "showed no interest in arresting people. They just wanted to shoot people, to hurt people," he claimed.

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