P Diddy took part in a hip-hop medley

Rap star P Diddy performed alongside 80s greats Salt 'n' Pepa as well as Run DMC and Naughty by Nature for a hip-hop medley, while one of the original stars of the MTV generation, Billy Idol, performed Rebel Yell.

But the extravaganza was without its original headliner Mariah Carey, who pulled out after suffering an emotional and physical breakdown last week.

It's very cool to have been there

Slash Guns 'n' Roses

The channel, which now reaches 342 million homes worldwide, began broadcasting on 1 August 1981 and is credited with playing a pivotal part in the development of youth culture.

"I remember many hours glued to the television set," said Slash, the Guns 'n' Roses guitarist, now aged 36. "I sort of grew up with it."

"It's actually an exciting event. It's very cool to have been there."

Billy Idol: One of the channel's original stars

The concert opened with cartoon characters Beavis and Butthead, who became cult figures on the network.

P Diddy - the hip-hop mogul formerly known as Puff Daddy - praised the channel for helping his career, while soul singer Mary J Blige said the network had helped artists like her reach new audiences across the world.

But Boy George - who was one of the channel's first stars with Culture Club in the early 80s - said it should go back to its roots and play more new and varied music.

"I think MTV has become everything it set out not to be. It's become a corporate monster," he told Reuters TV.

Jenny McCarthy: Former presenter was there

The network's original VJs - or video jockeys - were also reunited at New York's Hammerstein Ballroom for the show.

"It's like the MTV geriatrics have shown up," said Dan Cortese, a former presenter who has gone onto acting success in shows like Veronica's Closet.

Among the other veterans of the MTV era to appear were Joan Jett, Aerosmith and ex-Judas Priest frontman Rob Halford.

Janet Jackson, Depeche Mode, and Blink 182 appeared via satellite.

The concert was part of a range of special programmes to mark the channel's birthday, including a count-down of the best 100 videos of the last 20 years and MTV's 20 most outrageous moments.

TLC's performance was seen around the world

The list of the top 100 videos, compiled by viewers' votes, is headed by Fatboy Slim's Praise You, followed by Michael Jackson's classic Thriller and Eminem's The Real Slim Shady.

MTV's president of programming Brian Graden says the channel's success amounted to a "cultural and musical revolution" that few of its founder programmers could have imagined.

The channel now broadcasts to 140 countries in 17 languages including Cantonese, Dutch and Hindi.

There are five MTV channels in the UK alone, each dedicated to a different style of music - from hip-hop to pop - as well as showing non-music youth shows like Jackass.