Undeterred by rings of riot police, fencing and concrete road blocks, the protesters sealed off routes and road intersections by linking arms and chanting anti-capitalist slogans. Tear-gas volleys were fired near a freeway exit and a handful of protesters were seen walking through the streets with blood on their faces, but these incidents appeared to be isolated amid a generally festive atmosphere.
Several hundred delegates, scenting the tear-gas wafting down the hill towards them, were trapped in the Sheraton, the main conference hotel surrounded by a thick cluster of protesters. Dozens more delegates forlornly circled the convention centre area vainly searching for a way in to their meetings.
Some delegates were pushed and shoved as they came up against the demonstrators' lines. One or two became heated with police after they asked officers for help and were told to stay back. The opening ceremony of the WTO meeting did not start on time, and unconfirmed reports suggested it had been postponed by at least four hours to allow time for passions to cool.
With drums throbbing, whistles blowing and heavy rock blaring through the streets, the demonstrators pirouetted and danced, chanting: "Shut it down! Shut it down!" Environmentalists mingled with animal rights advocates, students with steel union representatives. "We ain't gonna leave till you get out of Seattle. Go home!" they yelled. Blockade points were clearly marked with spoof police cordon tape reading "Unseen Crimes" - a reference to the allegation that the WTO works in secret to promote the interests of multinational corporations at the expense of labour standards, the environment and human rights.
"Block the streets! They can't move all of us!" shouted the organisers.
The protest, which preceded a massive trade union protest and was not authorised by Seattle police, was overwhelmingly good-humoured and peaceful. A few dozen young people dressed in black clothing and black balaclavas appeared to act as a kind of praetorian guard, sprinting from protest point to protest point with gas masks, but they too appeared to shy from direct confrontation with riot police.
Uphill from the convention centre, a small group of protesters rolled rubbish bins and rocks towards a line of riot police. They were thwarted by two Caterpillar tractors that sealed off the street and soon backed off. Two early arrests were reported, but there were no indications of serious trouble.
Phalanxes of heavily armed officers, backed by squad cars and mounted police, milled in the streets next to the protests. Some made a show of brandishing shotguns, but generally they kept a surprisingly low profile.
It was the largest public demonstration in Seattle since the Vietnam War. With a whole cluster of issues at stake, from genetically modified foods to the rights of Zapatista rebels in the Chiapas region of Mexico, the slogans on display represented a kind of alternative globalism to that being pushed by the WTO itself.
"Fair trade, not free trade," said the banners, interspersed with whale balloons, large animal skeletons representing the threat to endangered species and big photographs of corporate leaders adorned with hate slogans.
Some protesters urged police and WTO delegates to join their protest. Others resorted to teasing slogans broadcast over a loudspeaker system: "WTO - You've been very naughty delegates. Go to your room." As the morning wore on, the numbers of protesters kept rising. A separate demonstration that started at the University of Washington a few miles away turned into a march through the city linking up with the main protest.
City officials did not appear over-anxious to clear the blockades and allow the WTO meeting to proceed. Seattle's mayor, Paul Schell, arrived at the besieged Paramount Theater, venue for the opening ceremony, and said simply: "You can be firm with your message, but be gentle with your city."
Protesters jumped on to the roofs of a ring of city buses set up by police as a barricade outside the theatre. But they climbed down after riot police threatened to remove them.
The protest, organised by the so-called Direct Action Network, began before dawn. Groups of protesters, typically sporting body piercing and coffee flasks, emerged with their banners all over Capitol Hill, a student area above downtown. Clusters came together and converged at a small park on the waterfront of Elliott Bay, near Seattle's harbour, before marching through the Pike Place farmers' market - a noted tourist attraction - and heading back uphill towards the convention centre.
"Whose streets? Our streets!" they chanted. Several banners played with the WTO acronym, suggesting "World Takeover Organisation" and "Way Too Orwellian". An older man in an Uncle Sam outfit had dollar bills pinned to his coat tails and symbolically swung at a football-sized globe with a baseball bat.
Speeches over the loudspeakers denounced the capitalist system and accused the WTO of putting corporate profits before people and the planet. Two men sprayed abusive slogans on the windows of a Nike shoe store, but again this appeared to be isolated vandalism. Most business were closed for the day, but some owners watched the protests nervously from upper- storey windows. Private security guards stood outside cafes, restaurants and shops.
Seattle, which hosted a famous general strike in 1919, was once again in a state of virtual shutdown. The port was closed and several groups of workers were on strike for the day, including taxi-drivers hoping to deprive WTO delegates of a means of transport.
During the late morning and early afternoon, tens of thousands of workers were to march from Memorial Stadium through the streets of downtown to demonstrate against an erosion of their rights and benefits. They were to be joined by several Seattle politicians who have been distinctly ambivalent about their role as hosts to the WTO. The proceedings were cheered on by various heroic figures from the heyday of 1960s activism.
They included Ken Kesey, organiser of the Merry Pranksters and author of One Flew Over the Cuckoo's Nest, and Tom Hayden, one of the so-called Chicago Eight who demonstrated against the Vietnam War during the Democratic Party convention in 1968.
"In 1968, we had one or two issues, but this is about everything," Mr Hayden, now 60 and a Californian state senator, said approvingly at a pre-protest gala celebration. Seattle's activist, pro-union side appeared to be outshadowing its more recent image as the powerhouse headquarters of Microsoft, on-line retailing, Starbucks coffee and other young manifestations of corporate culture. A photograph of Bill Gates on display at bus stops was adorned with the slogan: "Big Brother Is Watching You."
One Microsoft employee, trying to get to her office, shook her head and muttered: "This is crazy. Why can't they put all this in some field in Montana?"