A tense scene unfolded in Oakland last night as protesters, attempting to reclaim the plaza from which they were evicted early Tuesday morning, faced off with police—who used tear gas and percussion grenades on the occupiers.

The Occupy Oakland encampment in Frank Ogawa Plaza—renamed Oscar Grant Plaza by its new residents—was kicked out by Oakland police using smoke grenades on Tuesday morning over what authorities claimed were "sanitary and public safety concerns." At least 75 people were arrested in the process, and protesters say three were hurt. "I think we allowed people to exercise their rights to free speech and free assembly," OPD Chief Howard Jordan told reporters.

Watch Oakland Police Fire Tear Gas on ProtestersS

But the Oakland movement is one of the largest in the country, and as many as 1000 occupiers met this afternoon outside the public library to begin a march back to their plaza. The police had barricaded the plaza and threatened to arrest the protesters unless they dispersed; some protesters were arrested and others were tear-gassed. The crowd appears to be moving, but it's not clear that there's a direction.

You can watch a live helicopter feed of the demonstration on ABC 7's website here; there's another from the local CBS affiliate here. There's also this livestream from an occupier on the ground.

Update: Alternet's Josh Holland reports that 500 people have been tear-gassed; others on Twitter say flash-bangs and percussion grenades have been used as well. Live helicopter camera feeds from ABC and CBS were apparently cut off right before the police threw the gas grenades. (Update: They're back!) Left, a picture another video of tear gas being fired

Update 2: After the repeated tear gassings, Oakland protesters dispersed and returned home. They've said they'll return to the library tonight at 6 p.m.

Oakland Police claim that they were forced to use tear gas by protesters who threw bottles or otherwise attacked the cops. (This is certainly possible, though reports of aggressive or violent responses from protesters didn't start cropping up last night until well after the first reports of tear gas.) Zungzungu's Aaron Bady, who was there, writes:

If you read an account of the march like this one—or listen to the Oakland Police Chief here—you will get the impression that the crowd was the aggressor ("Occupy Oakland demonstrators clashed…with police" and that "The demonstrators sparred") and that "[OPD] had to deploy gas in order to stop the crowd and people from pelting us with bottles and rocks and…chemical agents that were thrown at the officers." It's very hard to see everything that is happening in a huge crowd like that, so the Oakland police chief may well be telling the truth when he says that his officers were "pelted by paint and a chemical irritant" But whether or not his officers were hit with paint—and even if that justifies what happened next—it has nothing to do with how or why the OPD (and officers from every police department in the area) first used the kind of force they did, when they did.

[...]

[At Frank Ogawa Plaza,] the police announced on a bullhorn that it was an unlawful assembly, they would use gas to disperse us, and that we would be subject to injury if we stayed. They said this very clearly - and I saw the front line very clearly at this point—well before the crowd had done anything but take over the intersection. And then the police did exactly what they said they would do. They were not reacting to anything other than the presence of a very large and angry crowd of protesters, who were at that point simply present. They said that if the crowd did not disperse, they would use force to disperse it, and they made good on their promise.

[image of protesters in cloud of tear gas via @Adreadonymous; video via ABC 7]