Large parts of midtown Manhattan were shut down on Saturday when an estimated 100,000 anti-war protesters took to the streets near the United Nations building.

An area of some twenty blocks along First Avenue was shut to traffic and patrolled by an unprecedented number of police personnel armed with guns, rubber truncheons, plastic handcuffs and riot gear.

The protestors ranged across an unusually wide segment of society, from  babies in strollers to senior citizens in wheelchairs, all of them braving 25-degree temperatures to protest the Bush administration's apparently relentless march to war.

Those who were barred entry by police to First Avenue, where the protest was centered, set up alternative hubs of activity along Second and Third Avenues.

Police spokesmen said around 50 activists were arrested. They said seven policemen and two police horses were injured in the rally.

Peace activists, meanwhile, decried unusually aggressive police tactics that left many civilians feeling roughly treated.

Cries of, "Whose streets? Our streets!" and "You are not heroes!" filled the air as protestors taunted the policemen.

Periodically, mounted police charged the crowd, injuring protestors.

In many places, activists spilled over the barricades erected to contain the demonstration. Some wore Bush masks, others were in outlandish costumes, small groups broke off the main mass setting up infectious poly-rhythms and singing, "Make love, not war!"

They handed out leaflets and peace badges, many protestors carrying cameras to record the moment.

Veteran folk singer Richie Havens began the protest with a rendition of the song he performed at the Woodstock festival in New York state in 1969.

The tune, Freedom, based on a traditional American blues motif, also started off the Woodstock festival. Havens reprised it on Saturday to roars of approval from the inter-generational crowd.

A number of celebrity speakers – from Bishop Desmond Tutu to Danny Glover and Pete Seeger – addressed the crowd near 49th Street.

"People are marching, people are demonstrating, because people are saying no to war!" Tutu told the rally. "Peace! Peace! Peace! Let America listen to the rest of the world – and the rest of the world is saying, 'Give the inspectors time'."

Martin Luther King III also addressed the exuberant crowd.

"Just because you have the biggest gun does not mean you must use it," he said.

At times the demonstration threatened to relapse into violence and disarray. Nervous policemen overreacted whenever demonstrators seemed to get too close.

One reporter for Discovery channel was pushed back by a group of policemen because she raised her arm to get a friend's attention.

"Who gave you the right to touch me?" she yelled. "Let me go, I have to find my dog!"

Priya Mohan, a legal observer and law student with the National Lawyers' Guild's New York chapter, said the reason the rally appeared chaotic was because the city administration had not adequately prepared.

"What else can you expect but chaos when the city reacts like this?" she said.

Mohan was referring to the fact that Mayor Mike Bloomberg made an unexpected last-minute about-turn by refusing protestors permission to demonstrate.

In fact, the city had made more than adequate preparations though much of it was invisible to the casual eye. There were snipers on rooftops with high-powered scopes trained on the crowd. Undercover policemen mingled in the throng keeping a close eye on any suspicious-seeming activity.

Authorities said $5 million was spent on security for the rally.

Traffic on the city's east side was badly affected. The Queensboro bridge, a major artery, remained closed for much of the day.

Barricades were erected in areas seemingly unaffected by the protest, causing delays and frustration to many residents.

New York was not the only site of protests today. There were demonstrations all across America and the world.

Estimates say 400,000 protestors marched in Berlin, about half a million people turned out to march against war in London, and more than a million people protested in Rome.

There were smaller protests in Philadelphia, Seattle, San Diego, Sacramento and many other cities in the United States.

Most where organized by United for Peace and Justice, a coalition of over 100 peace groups.

Soon after the rally was dispersed by the police at around 1700 (New York time), the site of the demonstration was covered by a seemingly endless barrage of leaflets, newspapers, garbage and horse manure.

Clean-up crews would be working around the clock to make the city presentable for business on Monday.