The video for Band Aid 20's single Do They Know It's Christmas? was shown on TV for the first time on Thursday.
Madonna recorded an introduction but did not sing on the record
Pop queen Madonna told fans to "feed the world" before the video got its premiere at 1755 GMT.
Madonna does not appear on the single itself - which is due to hit the shops in on 29 November - but recorded an introduction to its video instead.
It was shown simultaneously on BBC One, BBC Two, ITV1, Channel 4, Five, Sky One and other digital channels.
The video began with Coldplay's Chris Martin in the main hall of Air Studios, north London, where the song was recorded at the weekend.
It also featured some stars whose voices did not appear on the song - including Sir Paul McCartney playing bass, Radiohead's Thom Yorke on piano and Blur's Damon Albarn, who served tea.
And it included footage of organiser Bob Geldof in the studio playing the stars a video of an emaciated young girl in the 1984 Ethiopian famine.
Will Young and Jamelia duetted for their line of the song
The girl, now a young woman, was then introduced to the singers, many of whom were moved to tears.
Madonna's introduction began: "Twenty years ago, I performed at Live Aid and the world watched. You saw me and my generation demanding a change.
"Once again, here we are 20 years later," she said, over images of starving African children. "More people die of hunger in Africa than war and Aids put together.
"In a world of plenty, it is hard to imagine that most African children will go to bed tonight hungry.
"Bob Geldof and his friends are here to remind you that we can never forget. Not ever. Feed the world. I am honoured to introduce Band Aid 20."
The song, a remake of the 1984 original, was recorded on Friday, Saturday and Sunday by more than 50 artists including Joss Stone, Dizzee Rascal and The Darkness.
It is tipped to be the Christmas number one, but bookmakers have shortened the odds on the track's long-term success after it received lukewarm reviews.
The single, which also features Bono, Sugababes and Will Young, was made available to download from the internet on Thursday from a number of music services that will donate proceeds to the cause.
It is also being launched as a charity mobile phone ringtone with proceeds going to the Band Aid Trust, which is supporting food aid to the Sudan's troubled Darfur region.
Band Aid 20 - Who sings what
Chris Martin (Coldplay) - It's Christmas time, there's no need to be afraid. At Christmas time, we let in light and we banish shade
Dido - And in our world of plenty we can spread a smile of joy. Throw your arms around the world at Christmas time.
Robbie Williams - But say a prayer, Pray for the other ones. At Christmas time it's hard, but when you're having fun.
Sugababes - There's a world outside your window, and it's a world of dread and fear.
Fran Healy (Travis) - Where the only water flowing
Fran Healy and the Sugababes - Is the bitter sting of tears
Fran Healy and Justin Hawkins (The Darkness) - And the Christmas bells that ring there are the clanging chimes of doom
Bono - Well tonight thank God it's them instead of you
Will Young and Jamelia - And there won't be snow in Africa this Christmas time
Ms Dynamite and Beverly Knight - (Oooh) Where nothing ever grows, no rain nor rivers flow
Group of 10 and Joss Stone - Do they know it's Christmas time at all?
Tom Chaplin (Keane) - Here's to you
Justin Hawkins - Raise a glass for everyone
Dizzee Rascal - Spare a thought this yuletide for the deprived, if the table was turned would you survive?
Busted - Here's to them
Justin Hawkins - Underneath that burning sun
Dizzee Rascal - You ain't gotta feel guilt just selfless, give a little help to the helpless
Joss Stone and Justin Hawkins - Do they know it's Christmas time at all?
Tom Chaplin - Feed the world
Tom Chaplin and Chris Martin - Feed the world
Tom Chaplin, Chris Martin and Sugababes - Feed the world
Everyone - Feed the world, let them know it's Christmas time again (repeated)
Fran Healy - Wooo
Group of 10 - Feed the world
Everyone - Feed the world (repeated to end)
Joss Stone - Ad-libs over outro