2.50pm A fence made from 8 metal traffic barricades locked together goes across the street at the junction of St. George's Quay and Tara St, beside Butt Bridge. Traffic gets diverted across Butt bridge.
3.00pm Gardaí attempt to cut locks with bolt cutters. No good.
3.05pm Fire Brigade arrive with angle grinders and cut through locks, but a crowd of approx 800- 1000 people have made their way onto St. George's Quay and are now partying like mad things. Gardaí continue to divert traffic across Butt bridge.
2 sound systems are providing the music with decks/cds. A Rinky Dink Bicycle powered sound system is also present but is being fixed by Rinky Dinky engineers. Capoeira (Brazilian martial art) dancers have the crowd entranced with their street acrobatics. Other stuff: football, skateboarding, twister, dancing, bongoing, whistling, cheering, screaming, singing and guerilla gardening.
Medium / minimal police presence; no arrests, no hassle from the police so far.
Also a man is running around dressed in only a codpiece while hitting people with an inflatable mace.
4.00pm Party still going, no sign of abating.

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update:
4.10pm Some people attempt to push an old car (with smoke grenades going off inside) from a side street onto St. Georges Quay; Gardaí prevent them and some scuffles break out, some Garda wearing riot gear are present. One person injured by police now on the ground awaiting medical attention. People with video cameras (also some wearing press passes) have been dragged away from scene by Gardaí.
4.20pm Stand-off between crowd and Gardaí. Situation more tense now. Gardaí use batons, several people arrested, including one person on crutches.