The celebrities will take eight days to scale the mountain
By Kev Geoghegan
Entertainment reporter, BBC News
Nine celebrities who are climbing Mount Kilimanjaro for Comic Relief have been warned that several of them may not make it to the summit.
Take That's Gary Barlow, Radio 1 breakfast host Chris Moyles and Girls Aloud's Cheryl Cole are among the group tackling the tallest mountain in Africa.
People are being asked to sponsor the team on their 10-day trek, which will be shown on television on 11 March.
Singer Ronan Keating said: "They say a third of the team won't make it.
"I just hope we all make it up the mountain. It will really be tough on the team if one or two of us don't make it up. "
The eight celebrities will be followed by a production and safety team of around 120 people, which Keating hopes will make a difference.
Gary Barlow, 38, singer
Chris Moyles, 34, broadcaster
Alesha Dixon, 30, singer
Denise Van Outen, 34, actress
Fearne Cotton, 27, presenter
Ben Shephard, 34, presenter
Kimberley Walsh, 27, singer
Cheryl Cole, 25, singer
Ronan Keating, 31, singer
"There a lot of other people on the mountain with us, so I hope that it's their third rather than ours.
"I don't think people realise this is an incredibly hard thing to do, especially when you get above 3,000m."
Mount Kilimanjaro in Tanzania stands at an impressive 5,895m - nearly 20,000ft.
It is estimated there are 10 deaths a year among the thousands of climbers who attempt to conquer the peak.
Many attempts fail due to the debilitating effects of altitude sickness. Symptoms can include headaches, nausea and aching limbs, and the celebrities have been given warnings about what to expect.
GMTV host Ben Shephard said: "We can't second-guess the altitude sickness.
"We've all been training but none of us know how we'll be affected until we get onto the mountain.
"As soon as you get altitude sickness, people will start spotting it."
Cheryl Cole agreed that some were finding it harder than others, and said "the boys have been more affected than the girls".
Battle of the sexes
The other celebrities taking part include Cole's Girls Aloud bandmate Kimberley Walsh, Fearne Cotton, Denise Van Outen and 2007 Strictly Come Dancing winner Alesha Dixon.
Although they are taking part as a team, Walsh admits the boys are starting to take things very seriously.
The mountain-top is snow-covered all year round
She said: "There definitely isn't any competition between the girls, but I do think more so between the boys because I saw them in the gym and they were going for it.
"I was saying to the other girls that we might be up to the top first."
The climbers will have little contact with the outside world for the duration of the climb, which takes eight days, followed by a two-day descent.
Take That star Gary Barlow admits his wife Dawn, who gave birth to their third child three weeks ago, is not too clear on the length of the trip.
He said: "I'll be honest, I've not really fully briefed my wife yet.
"She knows I'm going, but she thought it was five days initially and I've kind of added a day on every month."
The celebrities are due to begin their journey at the end of February.