Police and fire officials battled for hours to put out several blazes started by concert-goers at the end of the three-day event, held close to the site of the original festival in New York state.

Several speaker systems were destroyed and tents were damaged as dozens of revellers danced around and through the flames while others beat drums.

Riot police then intervened to restore order. It is not yet clear if there were any injuries, and police say most of the 225,000 concertgoers have now left the site.

A fan dances in front of one of the bonfires

Trouble began at the end of the Red Hot Chili Peppers' set at the close of the festival. What began as several small bonfires escalated into several major infernos.

Police say several concert-goers set fire to 12 tractor-trailers, and others pulled cases of drinks and merchandise from the trucks and fed the flames with debris.

Others toppled speaker towers and light stands, while another group tried to destroy a truck belonging to a radio station.

One onlooker, Ruth Mahorn, aged 36, of Binghamton, said as she walked away from the disturbance with her friends: "These kids are animals. It should never have gotten this far."

Another, 24-year-old Karen Thomas, said: "They're jerks. It's been great all weekend. People were cool, and and now this is how people will remember Woodstock."

The original Woodstock festival marked the high point - in both senses - of hippy culture. Drugs, sex and wild dancing to live music helped define an era.

Before the trouble: Red Hot Chili Peppers' Flea performs

Now, rather than warnings about bad acid, the advice handed out at this year's anniversary concert was to drink lots of water - available free on site - wear hats and use sunscreen as temperatures soared.

"Rain rooms" - tents with sprinklers - were set up across the site and hoses of cold water were aimed at the crowds around each of the venue's stages.

In all some 60 acts performed at the festival venue, an abandoned B-52 bomber base in upstate New York.

They included Alanis Morissette, Sheryl Crow and Metallica. British acts included Fatboy Slim, Elvis Costello, the Chemical Brothers, Jamiroquai and Bush.

Soul legend James Brown opened the show on Friday, but only a single representative of the original collection of musicians who played in '69 is in this year's line-up. Mickey Hart, 55, formerly of the Grateful Dead was singing with his latest group, Planet Drum.

Click here to read BBC News Online users' memories of the original Woodstock festival.