Follow the Comic Relief team's progress with daily updates and video reports in our special feature
Three days into their Comic Relief fundraising trek up Tanzania's Mount Kilimanjaro things are getting tougher for the celebrity climbers. The stars were confronted with the enormity of the task they've undertaken on as they saw a gravely sick climber stretchered past on his way down the mountain.
As Cheryl Cole, Kimberley Walsh, Denise Van Outen and the rest of the girls reached camp after a day's hard climb word reached them of a man in a group ahead who was suffering from acute altitude sickness - a condition which can be fatal. They were left shocked and tearful when shortly afterwards, they saw him being transported down the mountain in obvious distress.
"It shook us all up," said pop star Cheryl. "You feel really strange at this altitude anyway, emotional and strange - then to see that really got to us. I started to wonder if I was suffering from it too - but I'm alright and we've got each other to help us get through."
The stars are now keeping a close eye on each other for any signs of altitude sickness. All seemed well as the majority of the group, including Radio 1 DJ Chris Moyles and TV presenter Ben Shepherd, successfully traversed the mountain's treacherous Cathedral Ridge on an acclimatisation trek. The section is so steep the celebs had to scramble on their hands and feet for the first time on the journey.
Take That star Gary Barlow, who's still suffering from a bad back, went on a solo four-hour trek over flatter ground in preparation for their ascent tomorrow.
The day had started out on a lighter note as the gang gathered together to sing Happy Birthday and present a cake to Ronan Keating, who turned 32 on March 3.